There has been some impressive progress with the P150 scratches and the two name cards but nothing official for neighbouring cards. Let's start.
There are a few ways to find these out.
front miscuts
double strike "ghosts"
known test print sheet mates
front overprint ghosts.
If you have any examples please post them.
Miller/Barbeau double strike & confirmed sheet mates.

Front miscut (Nice Willis Johnny!)

Test print sheet mates.