Funny to see the comments. "Back in the day" there were about 300 in the Band, in two outfits, Maroon Band and White Band. Before that, when ROTC was Army only, they were Artillery Band and Infantry Band, respectively. It was a little harder to know everyone in a unit of 150, but we managed. And we were also expected, as fish, to know everyone in the entire Band, not just our side, by name.
We're still pretty close. My closet circle of friends are my fellow White Band fish, but I still have a lot of close friends who were originally in Maroon Band.
In my sergebutt year, it was decided to split into 4 units to more closely match the size of the CT units. A lot of the motivation was to get more leadership opportunities and recognition for the cadets. For instance, the Band had very few RVs, because the RVs didn't seem to be interested in anyone who was not a first Sargent.
So in 1975-1976, when there were three 1st shirts (Maroon, White, Combined) we had 3-4 RVs. In 1976-77, all of a sudden we had about a dozen (A CO, B CO, A BATT, B BATT, Arty Band Staff, Infantry Band Staff, Combined Band Staff) It's not that the new classes were that much better than the old, it's just that the CTs were accepting them now that they had a position.
When we split into 4 units beginning in fall 1976, we also did a fruit basket turnover of personnel. Some former White Band guys went into one of the Batts, Maroon Band guys went in to the Infantry Band Companies. The idea was to defuse some of the old White Band/Maroon Band rivalries, and to enhance cohesion of the Band as a whole.
Human nature being what it is, the new rivalries redeveloped, and obviously the BQ outfits started naming themselves and adding mascots beyond the standard "A Company, B Company, etc.
I don't know when the 5th and 6th units were added or subtracted, perhaps someone younger can speak to that.