Les: I've read your list of ten, and can add a few more, from my own musical activities.
Unplanned impromptu singing in pubs.
Unplanned impromptu playing in pubs.
Non-folk festivals: eg maritime, canal, civic, general arts, rock, jazz.
Singing at family gatherings, parties etc.
Events not normally called festivals: eg agricultural dos, county shows, open days at garden centres, organic farms, food fairs etc.
Weddings, christening, funerals.
Teaching workshops(often unassociated with festivals)
Rehearsal groups: eg fiddle ensembles practising, that kind of thing.

Interestingly these sorts of things, surely the bedrock of folk as they represent folk in the community, rather than artificially and hydroponically maintained, do not appear much on the folk radar. A musician could be fully occupied playing folk music professionally full time, for example, and never appear in the Guardian or fRoots or on Mike Harding or whatever, because they are not playing within the folk ring-fence, ghetto, or whatever you care to term it.