It was a reputable brick-and-mortar independent store, with almost 20 years in the neighbourhood.
reputable isnt authorized...
Im a reputable loan bank to my friends, doesn't mean they can report me to the IRS as being a authorized loan broker.
Sorry to hear your loss here OP, i hate ASUS with a passion which is why i stopped buying products from them because there RMA just straight up sucks horrible dog dookie.
But on a good note, its better then Gigabyte, as they would probably have said sure, send the card in, and then physically throw it in the RMA pile in hopes some kind of physical damage will occur and deny your RMA and CHARGE you for the return on top... oh wait.... ASUS does this also.
But seriously, they are going by records of distribution which means your vendor source was denied and not accepted, hence they are going by manufacture date.
Also in cases of COVID, expect more shady RMA practices from 90% of PC parts vendors.
At least its not MSI, where they have even more questionable practices with service, as well as price hiking everything on the bases of "because they can".