Malcolm's comment
"Mind you, it can be quite effective playing a tune in G and then moving up to A; gives it a nice lift. Used to do that quite often. The better box players could manage the shift."
reminded me that this effect was used by a band of several friends of mine when playing at woolshed dances. I'm having a senior moment and can't recall the name of the tune just now but it was started in A and played a couple of times through, then a couple of times through in D, then a couple of times through in G and then the whole cycle repeated for the length of that particular dance, always finishing in A. It was usually known as "ADG", which is why I can't now remember its correct name.

The others in this group played ADG accordions, mouthorgans and whistle and the modulations were relatively easy. At the time I stuck to lagerphone and calling the dances but the set was often played at sessions and I was starting out on an Anglo concertina in D & G. Playing along with the others was the way I learned how to play in A. When we all went our separate ways the only times we'd meet would be in sessions at festivals, Most of the instrumental sessions I've seen at Australian festivals can be grouped into "the specialists" (Irish sessions are most often like this but we've had Morris, tangos, Macedonian, sth Queensland ones too) or "the generalists" where a wide range of tunes from all of the specialisms will be played. Some play the tunes three times though, some only twice and beginners are usually encouraged to strut out their party pieces.

Amongst all this I've noticed over the years that ex members of bands are quitely likely to reminisce in sessions. Occasionally someone will start a tune that everybody else recognises as part of a bracket that a well-known band has made popular. Sometimes it will happen because a muso recognises another face in the session as having been in that band and wants to stir them along. Such behaviour is often constructive but it needs a certain sensitivity to prevent it from 'taking over' and becoming an egocentric rant, as someone so eloquently put it. My own view is that I learned almost everything I know musically as a result of good sessions and I reckon I have an obligation to give as much back as I can to those who want to learn. Good sessions are a great way to give back.

And, once you've experienced a variety of types of behaviour at sessions, it's easy to exercise your discernment gene.

Cheers, Rowan.