Question

This relates to collaborations between a musician running 5.0 and another running 4.6.2 ...

Answer 1

Answered my own question by saving 4.6 before upgrading to 5, then creating a song in 5 and attempting to open that song in 4.6.  Answer is no, a song created in 5 won't open in 4.6 - you get a message about incompatibility due to the fact that the song you're trying to open was created with a newer version of S1.