If we have to force place a policy on a property that has been covered by a grandfathered zone throughout the life of our loan, don't we have force place for the current/accurate flood determination zone, since there has been a lapse in their grandfathered coverage?

Yes.

Somebody needs to contact these people and tell them if they fail to renew the grandfathered policy prior to the expiration of the 30 day grace period, it really could cost them big time.