The fact that, before I sent them back and got the corrected one, most episodes had a third of the screen having severe grain is horrific. This image was sharpened to showcase it but it's essentially what the issue was
They didn't even publically acknowledge the issue, just said to people who complained that they can send in and get it sorted free of charge.
BluRay is meant to be the pinnacle of quality, but S6 was atrocious. I got the 2011 Christmas special on BluRay, since I lost my recording and it looks like they've fixed the issue. There was zero grain, and I've not heard of any issues with the S7 Part 1 and S7 Part 2 sets, but it's possible that it can happen again, especially if there are 17 episode across 6 discs rather than 14