Very interesting stuff.
Does my PIO appear consistent in terms of size of markings you've seen on others? I mean each letter is very fat, like a paint brush was used, not a wax crayon. Thoughts?
As mentioned we don't have allot of 66 NJ examples of these markings to compare with. Yes they are much wider than I would have expected based on how the other marks were applied and how they were applied (as well as the results on term) at other plants. But we do still have the pitting/etching that suggests that the product was still a wax base and not a paint IMHO. If it had been paint the area would be smoother than the surrounding metal rather than the reverse we see in your picture.
Who knows. Maybe the worker was screwing around and ran is hand across, finger over or tried to correct a mis-mark
Maybe all he had was the short end of a crayon so he turned it side ways to do this last mark before he tossed it in the trash