I think you can see the USB serial number in the device manager, my guess is that the ones that are sticky (and generate new port numbers) will have serial numbers and the ones that reuse old port numbers don't have a serial number set.

Although you've also reminded me that port numbers will also change if the device doesn't have a serial number but is plugged into a different port....

Personally, I'd prefer windows to only use the physical USB port as the method for allocating COM ports, but then again I end up plugging in a lot of devices that behave as USB serial ports which probably isn't what most users do!

I too love the knowledge on this BBS! No question to big or small, somebody seems to have knowledge or an answer.