Newfoundland 256, Dropped Tool?

Back in 2018, I started a thread on Newfoundland 254 and various oddities on that one. There were quite a few plate scratches, and some ink drops. These stamps came from a large hoard collected by my Father-in-law, and most were on fragments of envelopes all from the Bank of Montreal. It seems that the bank sent out pre-stamped envelopes for their customers to return, so I had many, many copies of very common stamps, and all from the same source ... the Bank of Montreal mailing department. However, this gave me time to look through them carefully, and I was able to spot quite a few interesting varieties. I finally had time to expand into Newfoundland 256, Princess Elizabeth. Here is the normal stamp, in a block of 4:


The oddity is this one, and I have a total of 10 copies all with the same feature:


The lower right corner should look like this:


Instead, there is a large spot:


Now I might be convinced that it is an ink droplet that became smushed during the printing process. However, note that the horizontal line just above the spot is incomplete. Is it possible that there was a dropped tool or something similar to cause this?

These stamps (flaw and clean) is flaw on the New Zealand 1d Rose Second sideface issue is called the Screwdriver or Chisel flaw. Appeared in 1889 and continued for the next 8 years. Came about by the dropping of a chisel or a screwdriver onto the plate.