Now, what have we got here (guessing the cultivar of a red Japanese maple)?

[Piedmont Bonsai]

What great info in the aftermath. Thank you for all contributions.
Meanwhile I have found a another slip that says 'Nomura' as a cultivar. But I have to say, whatever it is, as long as the tree grows well, that is more of my concern.
And that I have found out, that the rich variety of this species is even hard to track by modern science (so far).

I wouldn’t say hard. It would actually be quite easy to do. It just cost a lot of money to sequence a genome and i don’t think there are any scientists that care enough to make this happen.