It has to be lol I used expired PR card to enter the border and that's how I can get my 2-year period started to count
I'm actually not familiar with the ATIP reports for border crossings (want to order one soon) and what info they disclose.
Again in theory, if you have that entry record and it
doesn't identify you as a foreign national (PRs are not considered foreign nationals), then to me that is rather a rock-solid argument that you are a PR/were a PR at time of entry.
[Hypothetically a PR could be 'reported' at the time of entry as not compliant and subject to potential renunciation - but that is not something automatic and contingent upon the PR's ability to appeal (and hence likely delayed for some period of time, months at least). And that PR would retain the right to work until the case gets to its final disposition.]
Sadly, you will still face the issue that you'd have to convince an employer of this logic, and they may not want to deal with such things.