I touched on this point before, but I’ll repeat it. Yes, a scrupulous vet should keep records. I am not trying to besmirch vets here (I am one), but you can absolutely pay plenty of people enough money to keep it off the record. I can also tell you that I know of at least a few circumstances in which trainers had “the regular vet” who saw them for all the normal, above board stuff that got turned over when it came time to prove vaccination, etc., and then the other vet who would swing by and do all the “irregular” stuff - maybe not illegal stuff, but things like an injection or two or maybe sell you that mystery bottle of compounded material out of the boot of their car - you know, the stuff with a name like “Max Red” that was compounded under the name of the vet’s dog…
An equine vet friend sent me a video of three vets discussing the myriad of “interesting” drugs they’d received for testing from thoroughbred stables. The presentation was actually to the Jockey Club, or at least some race association, but alas, I can’t find it at the moment.
(Edited for spelling mistake that messed up the meaning.)