To be fair, there are some great arguments as to why a single quad player is perfectly ok. Multi-thomm is a big supporter of having that voice in his ensemble, even if it means one guy...
A guy who goes by "multi-Thomm" wants a tenor voice in his ensemble? Surely you jest.

Then how exactly do they judge on how well the tenor player played his part, if they don't know what his part is?
The same way you do -- with his eyes and ears. You don't need a score to know if a line's playing well. You can see technique and hear things like cleanliness, blend, and balance without having the sheet music in front of you. Besides, if a field judge had his head buried in the score, he'd get trampled in the drill.