OK..I have tried to read all of the above, but will admit to just skimming some for key words. And I agree that this is a good topic to bring up now before it becomes an issue, however I see one simple clarification that could be made to the rule:
There is a quantitative difference between pre-built and purchased. Purchased means that the product has been designed, manufactured and built by a
Company as opposed to some other person/team/organization that wants to sell off robot parts. Correct me if I am wrong, but there is government (yes, I used that word

) paperwork which defines a company which then translates into taxes and what not. Also, if an organization becomes a company, they must pay wages to workers. And if anyone has ever added the hours it takes to build a robot and multiplied it by minimum wage....its not cheap.
It seems to me that if FIRST wanted to (or sadly needed to) clarify the rule they could say something along those lines to help them define "purchased". In this case pre-built would be anything a team made or purchased from someone other than a company before kickoff.
Eric