I'm having the same issues!
Most of my tassells are still green, soft and perky, and I pulled off one of the fatter cobs and it was still white inside and obviously not ripe.
A couple of them had brownish limp soft tassells, these were very tasty though probably could have done with ripening a bit more as the bobbles were still quite small.
I think a pet badger on a lead might be the best way of testing the ripeness! My neighbours who planted theirs earlier have had all of theirs trashed, and mine is still there [or was two days ago..]