Is online piracy a really serious problem? My opinion: nope.

[Occulus]

84. No, music directors have and are known to send to the publisher for a "review copy" of the score

which is then arranged without permission for the performance. This is because the canned arrangements for this or that piece are not necessarily balanced to the instrumentation of the group performing the licensed and copyrighted works. They might be written in an undesirable key, be too long or too short, have a bad transition from Part I of the show to Part II, and so on. Much of the time, the original holders of the copyright for the music have no idea that it is being publicly performed at all.

In particular, the drumline and sideline percussion scores are usually re-written in whole, because the publishers know jack about actual drumline parts. High school and college groups do this last all the time. Without permission, by the way, and in direct defiance of the "this music may not be altered or re-arranged without prior permission from the publisher" statement at the bottom of every last page. I have seen this done many times myself.

This was going on well before the internet became a matter of public knowledge, and continues to this day. Often, the performers themselves are fully cognizant of the fact that the parts have been completely rewritten.

"High School Bands don't generally march to some notes joted down by somebody on staff paper."

On the contrary- that is exactly what many of them do- the good ones, anyway. The music is rearranged to a fare-thee-well. Without permission.