Why aren't all of my Timeline Item Types showing up when I try and sync with Scrivener?

I’m reworking my Scrivener and Aeon setup to both cover writing prose and worldbuilding. So I’ve created a lot of different item types so they can all interelate, and also have their own folders and pages in Scrivener. But when I went to try and sync things up, not all of them are appearing.

Am I missing a checkbox I need to click for it to appear? Or a setting that I need to allow? Or is there a limit to the number of Item Types?

Ok, it seems like for some of my items I had taken ‘default’ item types and renamed them so they wouldn’t just be sitting there, but that causes some issues with syncing, and what can be changed in the options.

So it seems I should usually/always make a new type, instead of changing an old default.

Leaving this up for others, and maybe for the developers to allow some way to be able to change the defaults at a later date, or be able to delete them if they aren’t needed.