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I'm surprised that you didn't get PPR. Ottawa used to request PPR to catch cases such as these. An applicant who legally changed her name but applying with a passport with her maiden name used to be one of the triggers for PPR. But it seems they have stopped asking for PPR these days and go straight to DM.
 
Well I didn't legally change my name on anything till after I had applied by about a month or so. Not even my SSN. Because we had just gotten married. How would that be a red flag?

Is a decision made in just a few days normal or odd?
 
It's not a "red flag" as in anything to worry about. But CIC has (in the past) asked for PPR for people who changed their name when they got married but applied with a passport using their maiden name to avoid logistical issues because COPR will have whatever name is in the passport you applied with and also that passport number. They just double-check to see if you updated your passport or not.

My wife was in the same boat when I sponsored her. She didn't update her passport right away (she changed it about 2 months later) so she applied using her old passport with her maiden name though she changed her name after marriage. After she got her new passport, she e-mail Ottawa a scanned copy of her new passport. She still got PPR away and she e-mail Ottawa a scanned copy of her new passport. When she got COPR, her name and passport number matched her new passport.

going from DM to getting COPR can be fast. My wife actually got her COPR one day after eCAS updated to DM. Others have waited up to a month. It depends on things like when the case officer updated the system, when the system synced to eCAS (which happens once a week), where COPR is getting mailed to and so on.