So, for all this has turned into a long-winded whinge-fest, did you actually ever bother to discuss this with the butcher, or are you gonna spend the rest of time going on about it?
My experience with butchers has been good. Most cannot be bothered to steal from their customers, they have work to do, and a cooler full of better cuts of meat that they can choose from, if they are not so sick of seeing the stuff as to want to eat fish instead.
I know a few customers that got back a heck of a lot less than they should have because of the condition they brought it into the shop, in. Like, if it dries out while hanging, until the outer surface is essentially jerky, most of it is going to be trim and dumped on the floor. But you know, that can't possibly be the fault of the guy that brought it in, eh?
And geeze, what're ya doing leaving the tenderloins in the carcass for anyway?
My bet, the missing one got cut up or torn up on removal and ended up in the stew meat or burger. Can I prove it was? Nope. Can you prove it wasn't? Nope. If the cutter really is crooked, and a thief, so be that, there are ways to follow through with those too.
Cheers
Trev