Hi Clive welcome to mudcat. My take on what a 'session' means were deliberately oversimplified. There are of course crossovers. I have been to the sort of sessions you described above. I find a lot of sessions tend to be variable depending on who is there. We have regular sessions here Southport and are mostly instrumental with a few songs (if there are any singers present). I find that the best mixed sessions are to be found at Morris weekends when you usually get a mixture of singers & musicians. As you well know having spent time in the Scotch Piper, Lydiate when you were guests at the Southport Swords weekend of dance.
Cheers
Les