My guess is that we're up against the dreaded Minim Letters ...
If you write letters like n, u, i, m in medieval script, or in cursive sometimes, it's very hard to tell them apart; the word 'minim' is a prime example if you leave the dots off the i letters, and those dots are a late development.
Which is why our intelligent ancestors often substituted an o for a u or an i - to make it easier to read. That would certainly help for
Monroe! As it did for Home (instead of Hume), and women, which was sometimes written as: wymmen, but that never caught on.
Nice little thingies, minim letters - once you're alert to them, they pop up everywhere.
All the best