Welcome to the forum Ed. Many router collet nuts will turn freely when loosened and then tighten up again. If you continue to loosen the nut with the wrench it will start to turn freely again and the bit should be removable then. If it isn't you can try tapping the bit downward or sideways but be careful not to hit a cutting edge. Carbide is brittle and doesn't take impacts well. The 3612 was a good router and was used in many industrial shops.
Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.