Concert Going Mirage

Every year there is an event called the International Musicians Seminar which is held at Prussia Cove, here in Cornwall. I know thet they put on local concerts but I have never been to one. So this year I have booked tickets for a Sunday afternoon concert in Porthleven. Which be quite near us.
It will be good to go and try it out.

Except I do not know who is playing.
Nor what they will be playing.
.....Now I see there is a "NB" on their diary next to the "Time" of the concert... but no explaining what that NB be for....

It do get mysteriouser and mysteriouser.... will the venue disappear in a puff of smoke before I get there, do you think?