Seeing the various discussions, pointing out microscopic analysis of small corners of various stamps, made me check out Re-Entries.com and try to find my own. I found a few that have a very, very slight chance of making the list, but this Great Britain one really stood out to me.

The bottom line extends across the stamp, but short of the right corner.

The right line extends the height of the stamp, just beyond the top corner. I hope that these are more than un-erased guidelines.
