Ian Price has clearly stated American copyright law as he understands it.
Any others out there want to state it for their country ?
The problems are obvious.
Pillings hold that not only their diagrams are copyright but that their
notation is also. Lawyers acting for Pilling have recently written to
Dunedin Dancers requesting that they stop supplying Pilling-style
diagrams with their books of dances.
I'll keep you posted with any further developments on this.
For teaching dances :
Original instructions are usually (not always) best.
Original instructions plus devisor's notes _are_ best.
For learning dances :
Trained tuition is best.
Original instructions (plus devisor's notes if available) come next.
Cribs and diagrams trail in a poor third.
At dances :
However you can get the dance into _your_ head (different people learn
things most quickly in different ways) is best. Briefings, cribs and
diagrams are all ways of doing the same thing - each has pros and cons
but these are personal. I know people for whom each of these methods
suits them particularly and they can't cope well with the others.