AMD doesn't have a reference rx470 it's a bullshit hack made by the card manufacturers and the MSI cards I got are all garbage and I have to RMA all of them, the ones with Hynix ram are non-functional and the Samsung cards no longer work in 32 bit mode. The fan is screwed on the remaining armor card.
FUCK MSI AND FUCK HYNIX AND FUCK YOU TOO ASSWIPE, ARTIFICIALLY REDUCING NOTHING.
Once again, you must be doing something seriously wrong to kill that many cards in such a short span.
There is no way you received 7 "defective" cards of multiple models.
Hynix memory RX 470s work just fine, most will do ~1900mhz or so without memory errors, the occasional one will handle a bit higher.
If you cannot figure out what you did wrong, you'll probably end up killing the next batch too.
My suspicion would be some issue with power supply and/or risers.