Hi Kenny,
Although the document you linked gives the numbers you are refering to as its serial, i.e. 60101, it is in fact its squadron code. Mostly a five-digit number is used in which the first three digits indicate the squadron the aircraft is flying for and the last two indicate a unique number within the squadron. This code is not unique for a single aircraft. The unique identifier for the aircraft is the one detailed as RTAF serial and as you state the unique serial is written in the Thai language although in publications such as databases, the digits are written Roman style.
Alan