No doubt we will now hear everyone's Uni days stories or previous jobs or obscure publications or dictionaries to justify the word as being so well known.
Ah, yes! I have such fond memories of the
Schuss your own Adventure books.
In the 10 billion+ word NOW corpus
schusses has 3 hits only.
Schuss is used somewhat more often, especially in Canada, but it isn't common by any means.
I'll make
schusses rare. Also
schussed and
schussing, which have been common up till now, but possibly never appeared in a puzzle.
For future reference,
schussboomer is also an acceptable rare word.