The ever increasing USB COM port numbers is either a blessing or an irritation depending on how you look at it. Windows creates a new USB device port for each unique vid, pid and serial number that it sees.

This has the advantage of the com port number being "sticky" for a particular device, but becomes a problem if you are just testing devices to make sure they function correctly, you can soon end up at stupidly high COM port numbers that never actually get seen again.

If the device does not have a serial number or all devices have the same serial number, then they'll all have the same COM port number, unless more than one of them is plugged in at the same time, in which case it will be random.

And don't get me started on the "Microsoft tax" which you have to pay if you want a CDC device to be enumerated without the need for an INF file, even though you're using the built in windows and standar USB device class.....