I did a google search and found a little book that lists many, many Latin abbreviations and symbols used in medieval Latin (this is much earlier than the time period I am looking at now).
In the process I’ve learned a bit about the different declensions (1st, 2nd, 3rd), and the various cases. Some names are declined (not all are in the same declension!), and some are not. A bit of this I knew, but now know more.