Another excellent post. I agree with all of it, but especially the line I quote above.
I did want to add the following observation.
Originally, I interpreted that quote to mean:
"If your situation is so bad that 250+ pages are necessary for your file, then you have a credibility problem with IRCC." - actually no one can think of a serious, non-contrived example of this. (So it's unproven at best, and I'd go as far as to argue that we can consider it untrue unless and until a counter example is found proving it.)
After lots of back and forth (likely because of my thick skill), I eventually realized that this is closer in meaning to what the author had intended:
"If you think you need 250+ pages, it's a possibility that you may end up creating a credibility problem for yourself with IRCC, and you'd almost certainly cause your application to get delayed even if no credibility issues arise." - which seems quite plausible. Also, we have a real life example of this posted to the forum, so perhaps we'll get an update that provides a data point on this.
But now you've come up with a third meaning:
"if IRCC has concerns, meaning IRCC is questioning whether the PR's physical presence in Canada is less than the PR has declared in the application (in an application declaring RO compliance based on physical presence), there is clearly, at least to some extent, a credibility problem."
In fact, although undoubtably correct, this is quite divorced from the original quote. Here's a hypothetical example,
Say CBSA/CBP records are somehow incomplete and an entry record is missing. However, the timing of that entry is important - if it happened the day the applicant said it did, then the applicant meets RO. But it's possible that the entry that's missing missing from the record say happened a couple months later, putting the applicant below RO.
I think it's reasonable that IRCC then asks the applicant for some proof of documentation of the trip (and applicant is able to provide a copy of a taxi receipt from that day or a copy of the bus ticket, etc). It's technically true that there is "a credibility problem" but it's not the applicant's fault, the issue lies with CBSA's own system for having an incomplete record.
Also, in this hypothetical example, this is at most one or two additional pages needed (upon request by IRCC) - nowhere near the 250 number that was an essential part of the original quote. (Although the earlier statement "Including additional information and evidence in the application will not avoid complex processing." addresses that bit quite well.)
I might just be being overly pedantic here, as your overall post agrees with the middle meaning (thus we're all aligned and in agreement) - I'm just observing that your statement affirming that "a credibility problem, at least to some extent" exists, may be affirming something slightly different than what the author of the quote originally intended.