Very interesting regarding the advice from Seymour, mine has a cluster of 8 or 9 pinholes. I would have thought felt marker on glass would rub off. Getting a good density of correction fluid might be interesting as the last one I used was very watery.
Ive gone over to using a Lacerta Herschel wedge but also have Baader solar film filter which has no pin holes in it at all.
I wonder if the coating degrades over time