Agreed, but it is what it is. I had long believed that a U.S. citizen's travel history was likely not complete, since CBSA [apparently] never tracked exits from Canada for U.S. and Canadian citizens prior to ~June 2019 (by land) and ~June 2020 (by air). Even now, they don't really track exits; they get entry records from CBP and/or passenger manifest data from an airline. That, in essence, constitutes an exit from Canada...but when I personally called CBSA to inquire (recently), the officer's reply was "
I've never heard of that".
You should start piecing together this puzzle now. Flights are easy to retrace, but those day/weekend trips across a land border...not so easy. I would hope that once you have shown that the R.O. has been met (by eclipsing the 730 days in Canada benchmark) the other data may not need to be exact, but...who really knows. Since you have to state that
all of the information in the application is true and accurate, I would suggest that if you do not recall 100%, include a short statement attesting to that.