The glue (normally animal glue) from old doors tends to have lost its effectiveness after a few years, what generally holds the doors together is the wedges not the glue. Regarding the swelling of wood this is caused by the doors being in fluid, oblivously the longer the timber stays in the fluid the more swelling you'll get. Regarding the raising of grain there are 2 different reasons that it occurs 1. if a door is left in a tank too long which most, not all, people seem to do or 2. if a door is in a sunny spot for a few years and was naturally finished then painted this causes a door to look like a teddy bear.