Well, I'm down to test stuff if/when you need some test monkeys. It looks like there is a header that can be used for flashing (~.050" pitch 5x2 between the fan header and bios chip itself). Are you using this header or clipping directly to the chip?
I tried testing continuity on those pins, but i couldn't seem to find any that were common to the SPI flash pins. I might have missed something though. Maybe they are instead for JTAG or some other interface?
@Danlopez1222 Don't know if this is helpful, but while gathering stuff to prepare for bios flashing, I noticed that my Asrock B450M Pro4 motherboard uses the exact same IC for the bios flash. Maybe this is an indicator that the A300 and the B450M share similar functionality in the firmware?
The flash-chips themselves aren't really an indicator of anything major. They are all pretty much interchangeable between boards as long as the capacity is the same. It's easier for the OEM to use the same part across multiple models.