Here's another quote from the current rules,

"If weight is being enforced then all planes competing in that class must be weighed before the same round (round 1 or otherwise) for a baseline."

I read that as regardless of the Finals, unless all models in the class are weighed, the rule cannot be enforced.

The rules are really very poorly written. It says "Aircraft qualifying for a Final" when in fact the aircraft don not qualify. The pilot does. Last year a finalist in Masters used a borrowed model. Perfectly fine to do, but that model did not qualify for the Finals.