Hi Lydia, each of these are examples of custom hand-drawn lettering. You can see quite a bit of variance from letter to letter, which you would not see with a reproducible letter set or font. Prior to the late 1960s there were only a handful of metal letter sets available for reproducing an alphabet on a memorial, mostly made available by the Spacerite Company. The inscription would be transferred from the metal letters to the sandblast stencil via rubbing paper and would then be cut by hand and sandblasted–or in the case of hand-chiseled lettering, the inscription would be drawn directly on the stone and then chiseled.
After the stencil press was created in 1968, many more alphabets became available to use as plastic letter sets, some of them being borrowed from common print industry fonts. So, much of the more unique looking lettering you see on older headstones was likely custom work.