What does NX.G7WAA.001/006/008/011/015 signifiy?
These are the part numbers of the models e.g. NXG7WAA.001 Aspire R5-471T-51EE etc.
Are you saying that these differences convey newer or older models of the same computer?
Yes The OS or/and software releases generate new "models". It's neccessary for the support. E.g. Windows 10 Anniversary, when you buy the factory recovery media...
PS: I'm not an Acer employee.