Saltgrass.
I am old enough and wise enough to not worry about eating my hat. As a result of your suggestions, I had to go into the BT settings to be sure you were totally wrong. I managed to find a way to make BT reserve the port I wanted before installing the adapter, as a result I could then use it for my device. I couldn't do it the way you were suggesting, but I created COM4 first, then W7 used COM3 for itself, then I deleted COM4 and added my device and lo and behold it worked. I would not have done that without your suggestions.
So... I am enjoying this fine old hat !!
Good luck and thanks for being a persistent guesser.