Seems consistent with them being stacked post silkscreen or laser marking.
This really isn't the venue for this, you should be talking with your ST sales rep/channel via your buyer.
>>.. is it acceptable
Do the parts function in the circuit? Does some cosmetic marking on the underside of the package interfere with use/operation?
Your in-bound acceptance process should be able to determine if you're willing to accept/reject these based on criterion you've set in-house.
