I’m not aware of a map of description codes to categories (will check to see if I have one) - probably the quickest thing is just to make a few tests e.g. identify companies with filings of the type you’re interested in, retrieve the data and check!
Yes - possible categories are given, but not the full extent (as noted in the unofficial CH guide - e.g. persons-with-significant-control and confirmation-statement).
Is there any other source that you would recommend?