As a followup to my own message, I've contacted CIC again. The agent noted that my AOR which said "in-Canada" class was consistent with their file, but that after I called on November 19th a note was added regarding the incorrect classification. This was received and processed on the 28th, at which point my application was properly filed as outland. This should not in theory affect processing times, as the sorting time for sponsorship approval is allegedly by date of original receipt; my sponsor can follow up with Mississauga after the application processing time guideline notes applications post-October 23 (the noted receipt date) being processed.
With this information, I'm unclear as to how precisely the prior agent saw it had been assigned to or marked for Ottawa.
This suggests that anyone who received an AOR that improperly said "in-Canada" should promptly contact the CIC call centre. It seems unlikely that CIC would have noticed the error on its own until the file was erroneously opened as an in-Canada class application, after some absurd number of months.