Blue Devils used to march 5 tenors (mid 90's). I think recently however they have gone with 4 simply because of cleaning responsibilities. It is a lot easier to clean 4 than 5. Also, this year they are only going to be marching 8 snares to go along with the 4 tenors.
oh, and there is no telling where the extra person is used. They could put them anywhere...pit, hornline, or guard. Unless you know the numbers they marched compared to other corps...there is really no way to know.
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<-----Ryan Patrick Smith
Proud Member of Future Drummers of America