Short Observations:
(essentially concurring in observations already posted by others)
An isolated, minor mistake in declaration of travel dates, ordinarily will not cause much concern let alone, by itself, trigger RQ.
So-called "missing stamp" likewise will not ordinarily cause much concern let alone, by itself, trigger RQ.
Longer Explanations:
Regarding isolated minor errors in travel dates:
(such as one day off in reported return date, due to arrival just before midnight but actual entry into Canada, that is date customs is cleared, being after midnight)
Obviously, error-free is best. But most of us make some errors.
In particular, isolated instances of minor errors is very common, which is something IRCC personnel generally understand. These ordinarily do not cause concern. These alone would rarely trigger issuance of RQ.
Even during the 2012 draconian RQ sweep, when during part of that period more than a third of new applicants were being issued RQ, and there were several harsh automatic triggers for issuing RQ (for example, any applicant who made even just one trip abroad, and whose work-history included any period of self-employment or unemployment, was automatically issued pre-test, pre-interview RQ), one or two minor errors alone did not trigger RQ.
That said, different people have widely varying ideas about what constitutes a "minor" error. For context, we know that when OB 407 (April/May 2012) was implemented and for a long while after that, three minor errors did trigger RQ, and errors adding up to more than a small number of days also automatically triggered RQ. I forget what that number was -- best I can recall I think it was four or five days. What constitutes a "minor" error which is not problematic these days is probably a little more relaxed than that, but perhaps not by much and obviously the more numerous or the bigger the error, the greater the risk of RQ.
For example, I would suggest that omitting a week-long trip abroad is not a minor error. Whether that one error alone will trigger RQ I cannot say, but no crystal ball is necessary to discern such an omission elevates the risk of RQ considerably.
As others have already suggested, the significance of any error also depends on context, other factors.
Beware self-interest bias regarding what is "minor." I am reminded of the scores of PR applicants with history including a driving under the influence charge, referring to that as a "minor" offense -- no, just because an offense does not constitute serious criminality does not mean it is a minor offense. Canada considers such charges to be quite a bit more serious than "minor." Similarly I have seen both actual cases reported in official decisions, and a number of anecdotal reports in forums, where applicants refer to omitting a two-week holiday, or even longer, as a "minor omission." NO, no. Imagine your employer omitting two weeks worth of your pay. Not "minor," not at all.
Summary: Obviously, error-free is best. Isolated minor errors should not be a problem. Almost as obvious, multiple errors, even if minor, are more likely to be problematic.
The so-called missing-stamp:
A decade ago or so, missing stamps loomed large in RQ and residency cases. But for many years now policy and practice at Canada's Ports-of-Entry has resulted in a dramatic decrease in passport stamping for returning Canadians. In more recent years, stamping the passport (for a returning Canadian -- remembering that PRs are "Canadians") has probably become the exception, and probably by a big margin. (Going back to 2009 even, I re-entered Canada as a PR without getting a stamp scores of times.)
Thus the absence of a stamp recording a return to Canada is, typically, NO longer really a "missing stamp." Thus, typically, the absence of a entry-stamp ordinarily will NOT raise any concerns let alone be problematic enough, by itself, to trigger RQ.
That said, "missing-stamps" are still, at least ostensibly, identified as an issue in some cases:
That said, there are patterns regarding who and when a passport stamp is still entered, despite how often they are no longer entered into the traveler's passport. IRCC officials are typically well aware of these patterns, the situations in which a stamp can be expected in the PR's passport.
In such circumstances, those in which IRCC expects a stamp, its absence can raise concern. How much concern probably varies widely depending on a lot of other factors, including the overall impression and strength of the particular applicant's case.
Reminder: the main reason a missing-stamp (a truly missing stamp, not just the absence of a stamp) raises concerns is that it suggests the possibility the PR could have been using another Travel Document or passport, one not disclosed to IRCC . . . suspicion of this tends to be very serious, for multiple reasons, merely having any such other TD itself suggesting the possibility of unreported travel looming very large.
Additionally: Additionally, it appears that if for some other reason an IRCC official has concerns, the interviewing official (be that the citizenship officer responsible for the case, or just an interviewer if being interviewed by someone other than the citizenship officer) conducting an interview may employ questions about so-called "missing stamps" as a wedge or foil for the purpose of asking questions about the applicant's travel and time in or out of Canada.
In other words, there might not be any real concern about the particular absence of a stamp but its absence can be a jumping off point for questions, a way for the interviewer to probe more extensively into the applicant's accounting of travel and time in Canada.
While I cannot recall how long ago the so-called "missing stamp" issue last arose in an actual case reported in the official decisions (I have been at least scanning nearly every official citizenship case decided for many years now, allowing for perhaps occasionally overlooking one or two), it was not too long ago. CIC or IRCC would likely deny their focus on the issue, in those particular cases, was not really about the import of the missing stamp itself, but it is readily apparent the real issues were more about underlying credibility concerns, and the "missing-stamp" was being used to make a case for challenging the applicant's account of travel.
In other words, my opinion, my extrapolation from scores of cases going back a decade now, is that the absence of an entry stamp is, itself, no big deal, not at all, and will not really be the reason why IRCC issues RQ, and not a reason for IRCC to have real doubts about the applicant's case. But IRCC might hang-its-hat, so to say, on such an absent passport entry-stamp if other aspects of the case cause concern leading IRCC to want to review more detailed information and objective documentation supporting the applicant's case . . . that is, to issue RQ.
In other words, even if it appears IRCC has concerns and issues RQ due to a missing-stamp, my strong sense is that (probably) there are other reasons for IRCC's concerns and that RQ would be issued in that case even if there were no "missing-stamps." . . . especially if IRCC has any concern about the applicant possibly having some other undisclosed TD/passport.
To be clear, the above (regarding import of so-called "missing stamps") is not based on any authoritative source, but is my opinion derived from my own analysis (I try to distinguish my observations based on sources versus what amounts to my opinion, so anyone interested can make up their own mind about it).
Credibility, Credibility, Credibility, Credibility, Credibility, Credibility:
All the specific, technical requirements are important, of course. Eligibility is dependent on meeting the specific requirements. Beyond that, however, the next most crucial aspect of any citizenship application is the applicant's credibility.
The importance of the applicant's credibility cannot be overstated.
There tends to be, among some, a misconception about what credibility means. It is not just about honesty. To be sure, if IRCC perceives any reason, any reason at all, to doubt the applicant's honesty, that will be problematic. Any hint that an applicant has been willfully deceptive or even evasive will be problematic, and if that is in regard to travel or ties abroad, RQ is not the problem the applicant needs to worry about, the outcome of the application itself will be seriously at risk.
Indeed, misrepresentation is a stand alone ground for denying an application and barring the PR from eligibility for citizenship for five years, as a minimum consequence.
But in the vast majority of cases where CIC/IRCC has had credibility concerns regarding the applicant, it is not so much about the applicant's honesty. It is about how much CIC/IRCC could rely on the applicant's reporting to be accurate.
Any mistake, any discrepancy, any gap in the information submitted, no matter how innocent, and indeed no matter how minor, constitutes an example of the applicant failing to be a complete and accurate reporter. None of us are perfect. IRCC does not expect perfection. IRCC is not concerned if there are indications the applicant is not a perfectly accurate reporter.
There is no precise formula for identifying what degree of error or omission or discrepancy will tip the scales toward IRCC having concerns about the applicant's credibility (the extent to which the applicant can be relied upon to be a complete and accurate reporter of facts). Indeed, to the extent there is any scale, it is undoubtedly a sliding scale.
And this leads back to another common refrain of mine: appearances matter; impressions matter.
I bring this up again, here, because many people want definitive answers about how this or that particular fact or circumstance is going to affect their case. Here, for example, there is a more or less emphatic desire to know if a missing stamp, or a date off due to clearing customs after midnight, will trigger RQ. There is no definitive answer to that. By itself, no, neither should trigger RQ. But then one can readily go find reports about cases in which such things appear to be a focal issue in a residency case. Which is it? Problem or not a problem. Does not work that way. Context matters. Appearance matters. Impressions matter. And the common thread here is that it is the applicant's credibility which matters a great, great deal.