Lotte is a short form of
Charlotte.
Lot is an even shorter form of the name.
They are not diminutives, because if they were, then they would have had one of the following suffixes: -ie, -je and -ke. Here are a few known diminutives of
Charlotte:
- Lotje
- Lotteke (you're more likely to encounter this one in Flanders than in the Netherlands)
-
Lottie (this one is also variantly spelled as Lotti and Lotty)
You can find all of them in the database at the website of the Meertens Institute, which I see you're already familiar with.
Oh, and I'm
Dutch, by the way. :)