There is pretty big difference in timeline of credible leaks for Nvidia versus AMD for past few major releases - AMD leaks start significantly closer to launch date. So the fact that there are no leaks for RDNA4 at this time does not mean summer release is too soon.

Obviously for the same reason release date is pure speculation at this point.

They didn’t. It simply this test from CB with their amazing Jedec memory speeds https://www.computerbase.de/2023-11/cpu-gaming-benchmark-2023-amd-ryzen-intel-core/