They were never grounded, the first waves were scrubbed/held and i imagine marham would have had thier own stuff to deal with.

It may sound insensitive but theres still a task to be done, so they wont ground the jets until its absolutely neccessary. As it stands, there is pretty strong (circumstantial) evidence pointing to what the failure was in this case, and it doesnt indicate a fault that would ground the fleet, its also something thats easily and quickly checked on the other seats.

The board of inquiry in this instance should be fairly quick, made easier by the fact that the airframe was recovered to base, there is only one component that can allow the seat to leave the aircraft in the manner it did, and thus they have a good idea where to begin looking.