yep, if you have ever filled out the Arrive Can Ap (not mandated at this time, now) they already have your vax status on the border crossing doc list, that they track you on. they have a written tracking online for every border crossing you have made in the last 20 years (or more). that is why they ask, when was the last time you crossed, they ask you where you are going, and when you are coming back. they look for inconsistencies in your trips, stories, claims of what you are getting, or brining, going to/from with you etc... when they see a pattern, or a inconsistency, it gives them "grounds" for a secondary search. your results may vary.
they scan your license plate and track that as well. they know who owns, or drives certain plated vehicles, this lines up with the passport, or ID provided at the window. they know who should be in that auto, prior to you even getting to the window. Ski