Barleywine
For the 4 x 9 I do not read the corners, but for the 8 x 4 plus 4 I do. Feels like I am doing math! So,with the 8 x 4 I read "1, 8, 25, and 32".
I am sure others have their own ways of doing GTs, so it would be interesting to see who uses corners or not etc.
DND
Since I consider the last four cards (33 through 36) to be a "stand-alone" part of the reading, I also read the corners as 1, 8, 25 and 32. To me they seem kind of like "stakes in the ground" that show the broad outlines of the reading, similar to surveyor's stakes that mark property boundaries. But I don't give them quite as much weight as I do the first three cards, and certainly not as much as the cards in the "near/far" complex(es).
The same question comes up with mirroring; I don't recall exactly, but it seems to me you aren't supposed to "mirror" to the last four cards in an 8x8+4 array. On the other hand, I do knight to those cards.