One more thing about those old album sales:
Yes, the Dave era sold more, but you have to take into account how many times the same people have bought those records over and over because of media changes and wear.
I had VH, VH2, Diver Down, on vinyl. Then tape. Then replaced all of those tapes several times due to wear. Then CD. Then the remasters.
The Sammy era only had one record, 5150, that wasn't released on CD to start with. Unless you lose or break your CD, it'll be a LONG time before you have to replace it.
Not saying that the Dave albums wouldn't have sold more regardless, but the figures would be much closer.