There's a story, i believe included as an extra on one of the TNG films or TNG seasons, don't remember which, that shortly after TNG wrapped, the Enterprise-D disappeared. It was discovered sometime later to be hanging on the ceiling of a Bar and Grill somewhere, whereupon someone stumbled upon it, contacted Paramount, which bought it back. That's probably why its so damaged. Or perhaps it was damaged while making Generations. But i remember hearing that a replica was created for that final scene where the Enterprise-D plows into the ground.