Description:

As far as we know:

If the serial number starts with M - it could be any device with LTE CAT1 or LTE CAT M1 modem.
If the serial starts with Q - it is a device with 2G modem.

The next 4 number means the year(first 2 numbers) and the week(next two number) of the manufacture

Some time ago (somewhere before 2020-2021) the first letter of the serial meant the device type.
So it was T for TCO4-HCV or L for TCO4-LCV, but later it was changed it.