call them they'll tell you how many tickets they have sold - that's what i did yesterday.

also, not all seats you can see online are already sold (sometimes)
here's how to find it out:
go on a random day in the far future, may 17th, enter your flght #, note which seats are taken, do the same for june 17th, note the seats
and then july 17th, note the seats...the X amount of seats that are always taken are the ones blocked by the airline....
is there a direct flight to your destination? that way you might get a voucher AND a direct flight if not, check in early and hope!