Repetition also seems like an huge issue given a 35,000 lyric limit. If someone repeats the same line 5-7 times it's hardly reasonable to count that when estimating vocabulary.

Edit: A quick check found 7 repetitions of the same 8 word phrase in a DMX song. Which I chose becase he was at the bottom of the list. http://www.azlyrics.com/lyrics/dmx/whatthesebitcheswant.html