is it possible I received an 512 MB upgrade (on an Intel HD Graphics 4000 that had just 512 MB) through the Apple store?
You mean to upgrade the GPU RAM?
the Intel HD 4000 has shared memory, so if it needs more memory it will use some from your system RAM. If you increase your system RAM then your mac will have more RAM for the Intel HD 4000 GPU...
You can find more info about the chip here: