let's see if these show up:
split grill (this is a quad - split in both directions)

and double grill

It's not bad if the grill bleeds off the edge of the stamp. It's better if the next one bleeds in from the other side (that's the split - you have pieces of 2 grill impressions because the grill was applied off-center and split by the perforations). The double has two different grill impressions on the same stamp)
These are on 3c copies, but all the backs look alike.