I think I figured out what's happening! 🙂
The official Memrise courses had two different versions, one for British English speakers and one for American English speakers. My Little Word Land has a single English category, so both versions of the courses are showing up there.
Ideally, I'd like to encourage people to use whichever version of the course was most popular, and then rename the old course to be something like "Italian 1 (Old course, for American English speakers)", so people know not to sign up for that one.
Long-term, I think it'd be great to have a system where course creators could have multiple versions of their courses, to support different dialects. I have some ideas for this 🙂