Due the the sheer number and types of MAI, certain classifications have been made to identify them much more easily.
The Millenium Number is the number that comes after the MAI's base four-digit Identification number, and it has a very straightforward purpose. There are obviously more than 9999 MAI in existence, so every time each number combination is used in IDs, a new Millennium Number is added and the numbers and cycle again. For example, the first batch of MAI's IDs had a Millenium Number of one, so it would look like "9999-1" and the second cycle for that four-digit ID would be "9999-2" and would refer to a completely different Unit.
The "True Generation" of MAI consists of any MAI that took part in a war. So as a given, virtually every MAI activated from 1979 to 1985 is a True MAI with a few rare exceptions. To categorize these MAI, an abbreviation is added to the front of their ID. For example, "TG-1624," TG (True Generation) being the added abbreviation. Things are made slightly more complicated in the event of another war, in which numbers will start to be added beside the abbreviation. As an example, MAI who fought in the Third World War would have "TG1," the next war would be "TG2" and so on and so forth. If a Modern Generation MAI happens to be drafted into war, their ID changes into their respective TG.
The "Modern Generation" consists of any MAI who is built to be optimal to take part in war, but has never fought/has not fought yet. Modern MAI get the abbreviation of MD (Modern Generation), and this abbreviation will gain a number after it after one group of MD and another are separated by a True Generation. This means that if "MD1" exists for a period of time then a war breaks out, after the war ends, any MAI built after the war is "MD2"
The "Faux Generation" is the only generation of "MAI" that under no circumstances gains a number after its abbreviation. This is because Faux MAI aren't technically MAI, but rather an LAI mimic of one. The abbreviation of the Faux Generation is "FG."
All IDs Considered
So with all things now considered, we can look at what full ID numbers look like.
Example 1; True Generation MAI, WWIII, first digit batch: TG1-8245-1
Example 2; Modern Generation MAI, after WWIII, tenth digit batch: MD1-3674-10
Example 3; Faux Generation, fifth digit batch: FG-2835-5
The IDs, classification-wise, are similar in that they have the structure of TG, MG, and FG, and the Millennium Number directly after their larger ID number, but are different in that they have a give digit base number and an "R" after their Millenium number. Considering this, here are some examples.
Example 1; True Generation MAI, WWIII, second digit batch: TG1-25273-2-R
Example 2; Modern generation, after WWIII, seventh digit batch: MG1-57496-7-R
Example 3; Faux Generation, twelfth digit batch: FG-11844-12-R