Yes, Mark, the 'relative numbering system' works well in group situations. I spent some time playing with a group who had printed word sheets with chords names on the top of each line. There would also often be a note 'up 3' etc - which was fine for capos, but was a little hard at first for a Piano Accordion Stradella Bass!

First I had to establish the real key (not always as simple as you may think), then translate the chord names to I, IV, V, etc then find the start point and range on the Stradella Bass. After a while with suffucuent practice of this new needed skill though, it becomes almost a reflex.

Cluin, yes, I've seen that too. There are a myriad ways of notating music.

Robin