Thanks very much Jon, actually there's a wide range of options for frequency: 2nd Thursday, 1st and 3rd, etc. Of course there's always the Maverick who goes for the penultimate Wednesday but there's an "other" box to tick if you refuse to conform (hooray for the non-conformists)
But if you know of an event worth supporting the map is open for a member of the public to add it so please feel free.