Crap, I think I just figured it out.
"Mathematical Alphanumeric Symbols*is a Unicode block*of*Latin*and*Greek*letters and decimal*digits*that enable mathematicians to denote different notions with different letter styles. The letters in various fonts often have specific, fixed meanings in particular areas of mathematics. By providing uniformity over numerous mathematical articles and books, these conventions help to read mathematical formulae."
"e.g. in mathematics an*italic*"A" can have a different meaning from a*roman*letter "A". "
So basically different handwriting can mean different things with the same letters. Handwriting varies by region and person, even now you have people who just put a line for 1 and those who have little wings to them. Or some put a line through the middle of Z while others don't.
So they had the stencils with the 'block' letters which make it clear to everyone what they are and then the letter markings in other handwriting would clearly be the italic ones.
Probably took way more time but it would make it easier to mark the works.