Don't forget the musicians need to warm up a little as well as the instruments. In folk clubs I've found it fairly common for people to play around a bit on their instruments before the proper scheduled events get under way. Many clubs don't have the luxury of a green room or space away from the main area, to tune up / warm up, etc. But most theatres do, so small band and solo artists will normally do this off-stage. But I guess it might be different for a large orchestra who would want to practice together. But I realise it would be highly unusual for them to do this on stage just before the actual concert. Maybe they were amateur players and had come straight from work or whatever?

What was the actual concert like? To me that would be the most important thing - I wouldn't care about what happened beforehand, providing they put on a good performance.

As for tuning, I always tune my guitars before I go out, then when I get there, then if I get a chance (and I don't always, depending on where it is) I check just before I go on. And of course during a set I occasionally have to tweak the tuning of the odd string or two.

I'm often surprised at how many guitarists tuen between different tunings on stage - I wouldn't want to do that, and would prefer to have more than one guitar tuned appropriately (but I realise there are often good reasons why this can't be done).

As for Martin Carthy, I don't know whether he's become less of a perfectionist with regard to his tuning, or what, but last time I saw him (a month or so ago) he didn't spend any more time tuning than any average guitar player (unlike the previous time I saw him where he seemed to spend ages between each song before he was happy with it).