Have other groups tried things like this?? Would a
pattern like "3rd
Sundays are contras, 1st Sundays anything goes" be too much
to remember?  Would it hurt our community, because people
come to expect one thing from BIDA (contras) would come to
expecting that and be disappointed?
You could think of it like dances at the Greenfield MA Guiding Star Grange.
Each Friday (or Sat) dance has its own flavor, in part because of who's organizing it.
Some people dance every Saturday night, others may choose.
Or you could think of it as if BIDA were organizing two different dance series.
(As you know, NEFFA does this with the Thurs night dance and the Family dance)
Third Sunday BIDA dance is a contra dance.
First Sunday BIDA dance is a wonderful variety.
Both are lots of fun.
You could even market/publicize them separately.
In any case, you can't be responsible for people who choose not to pay attention to
your clearly expressed publicity information.
(If they are disappointed because of misguided expectations, perhaps they'll tune in
more next time.)
Plus, they might actually be pleasantly surprised by something unexpected.