1612 and 1630 are pretty certainly fakes. Best bet would be the ones E-best is selling now. Make sure to confirm the 1001 date code. Last time they send me 0842 or something and they were remarked and did of course not work. Hopeless.....
Some chips were made new, most were not. 0752001 is a MASSIVE market for. Chips are mostly made for OEM repair, not for stuff we do.
0729051 was only used in a few machines, so why bother making them. Setting up a production line for these again costs 100s of thousands $$.
What about 2025 DC1512. This is one you wrote here that they are new. This is the only one we know?
Never had so many problems replacing GPUs as now with these iMAC. One of them had to replace the GPU 3 times and each time works 1 month. I dont know if there are sense to do that.