Okay, pardon my ignorant posts on what Citavi I've actually got.
Now that I'm on my pc I can see what's what.
I've definitely got the Citavi Free version, and from my reading of their
Products page I see that what they're saying about the Free version is that I can have 100 References.
Now I recall reading some time ago what 'references' actually means and will post when I re-find that info.
From memory the discussion goes along the lines of: a reference is not a project - but the number of references that a project can have. But I want to clarify that, because a reference could be the number of projects in total and nothing to do with references attached to it.
Anyway, it's suited my needs to date, but I don't have anywhere near 100 references. I use Calibre for all my ebooks, and just use Citavi for some of my reading projects.