One way is that they should come up red in the record, if they aren’t in the terms list. And the variation in full stops do make a difference (I just tested), although the first time I tried it with a style that removes them, so it “looked like” it was working, but it wasn’t, when I switched to an output style that didn’t removed the full stops (this is a journal setting in the output style). And yes, you can only have 3 abbreviations, but I don’t find this kind of variation very often since I usually download from a limited number of resources, so it is usually constant.
Remember you have to import the terms list for each library independently too, so if you use more than one library(and I recommend against that for this and other reasons) you need to add the terms list to each one, and to remember to change each one! At least you don’t have to change the preferences for each library (but do need to change those on each computer!)