Reason why seats are blocked is usually because TAs have been assigned those seats and they hold the block until X number of days before departure then they will be released or washed because the TAs didn't manage to sell those seats, or close the tour group booking etc.

OLCI is usually your best bet, or from 2 weeks before your flight, log in to see if any seats have come up. I usually do that for bookings I made far in advance to select my seats and usually manage to get something quite decent.