Often custom themes for Windows 10 are delivered in different versions, depending upon which Windows 10 build you are using. - How do the themes differ between the different Windows builds ? - Is there any (non-) official documentation available, describing the differences? - what happens if you e.g. are using a Theme made for Windows 1703 in Windows 1809 ? Does the whole system gets unstable or are there just "aesthetic" problems?
Not much, just Microsoft breaking things repeatedly. Themes have to change because of the way they change uxstyle, too. I couldn't use anything at all when I used a 10240 theme on 15063, and I had to use another user account to try to fix it. Spoiler: it didn't work.