These numbers are a little bit similar to mercedes Wxxx or BMW Exx/Fxx/Gxx (x mean number)The first place that comes to mind is Kempers used parts (kempers.de). Here is what their car / parts selection menu looks like:
View attachment 292923
i don't even see GTI in that list so i am guessing it is one of those model codes? Maybe? What is Variant?
i someone somewhere say 5G was the Mk7 and 5G1 was the Mk7.5, but i have seen other places that contradict that.
Why Kempers? My eight year old dreams of having various parts from our car (his sole reason for wanting to do mods on the car i suspect so that he can have the original parts). i look at places like that daydreaming of picking him up an EA888 to take apart. Yes, that's what he asks for his birthday, Christmas, etc. He wants to take apart our engine. Or a VR6. And then he will likely decorate his wall with all the parts.
In case of Golf, from this picture
5G - EU/RoW Golf 7
BQ1 - NAR Golf 7 (Made in Mexico)
I'm only sure about 5G (EU/RoW) and BQ1 (NAR), rest is more or less guessing
In VAG, most of these number are used for giving the parts numbers. If you check them, most mk7 golf parts use 5G0 xxx xxx pattern (5G1 xxx xxx gonna be specific, RHD parts), sometimes, in your car you gonna have different first 3 digits on parts, like 3C0, or 5N0, and that means this specific part was originally used in other car ( for example, some brake parts have 8V0 or 1K0 numbers, meaning that originally they were made for A3 8V or Golf Mk5 1K) In some cases the third digit in part number means body type (example from A3 8V: 8V0 is "common/universal" part, 8V3 3door, 8V4 5d sportback, 8V5 sedan/saloon, 8V7 cabrio/convertible)
In case of parts that have left/right placement, like doors, headlights,etc. the last three digits are odd or even numbers, meaning odd for left (LHD driver side), and even for right (LHD passenger side)
From VW parts numbers, you can decode many information, some rim as example:
5G0 601 025 CD FZZ
(5G0 means 5G golf mk7 chassis)
(6 means part group in ETKA catalog, in this case 6 means "wheels/brakes" group)
(06 means that part is in sub-grup 06, in this case 06 means "aluminium rims" sub group)
(025 CD is specific part number with CD being version or revision of that specific part)
(FZZ is color coding, in this case, "Brilliant alu/black")