5A and 5B are different boards. For now only 5B is available. 5A should be smaller, credit card size board with cheaper RK3588s. Sometime image for different CPU will boot, but it will have many issues and errors. Pay extra attention to right model, that saves lot of time 
Nvme software support at launch of rock 5b
Sorry for my slow response, but thanks for the info.
I realized my mistake soon this time, but as you said, I wasted half a day. Radxa’s policy, where they open the system software even before the product is released, is a bit interesting to me.