Kendall, you're the exception to many a rule! You can show up any time with whatever you like.

As for the definition: after going to 10 bluegrass festivals over the summer, I can attest that most bands consisted of guitar, banjo, mandolin, bass, fiddle. Sometimes there was a resophonic guitar (Dobro). Sometimes it was a foursome with guitar, banjo, mandolin, bass. Typically however, by far, it was the g-b-m-b-f combination with three vocalists doing melody, tenor, baritone, with an occasional bass singer.

Jams, however, are a different thing. Don't recall seeing any clawhammer on stage, but there was plenty of it at our jams. Didn't see any harmonica on stage, but there was occasional harmonica at our jams. We had a bluegrass saxophone once, cello, bones, autoharp, concertina, etc. The music was bluegrass.