My theory way early in either this or the other thread when someone posted about getting their stickers in under a month was they mixed up the stack somehow, getting a stack of applications that came last and processing them or processing in LIFO order.
However, from the talk about them still working from home, it could be possible they split up the stack in a way that might make the order different. For example they have 4 people working from home, split out in 1/4. The one who gets the last 1/4 stack would be processing applications that were much more recent. To make processing more even, they would have to make 4 stacks, separating them application by application, but I doubt they do that. Also matters how long it takes before they send a "batch". Of course, this also depends on the employees working at home making an effort to preserve order.