I don't know, Dan.
The motorcycles, at less than 40% of the entries, have by far the most classes, yet their entries seem to increase every year.
Their participation is witnessed by their pride, at other events, of listing 10 or 12 "records" under their signature with the same bike, usually in the same configuration, just filling a hole. Must be "old hat" to build a vehicle to take away a set record any more.
The SCTA car classes haven't increased in years -- except for the ill-advised Compressed Air Roadsters. That worked out well, didn't it? Loved seeing all those DeSoto, Studebaker, Olds and Cadillac-powered roadsters the last two years -- didn't you?
Stan