There is an excellent summary of abbreviations and general characteristics of variables provided by our good friends from Astronomical Society of South Australia.
UGSS = SS Cyg. A UG subspecies with outbursts lasting for several days.
I wonder if AAVSO might contact ASSA and see if they would mind either linking to their site or porting the content (with proper credit) to the AAVSO site. I have found this a great help when I look up other variables in the field of my intended target as the VSX uses these abbreviations rather than the formal names. I don't think such a summary is available on the AAVSO site and it tends to be scattered in reference books.
An alternative is to place the abbreviations and general characteristics in both of the new manuals.