RiP wrote:For example, this 72-pin SIMM has eight NEC 4217400-60 chips that should be 16MB but detects as 4MB only.
The mainboard may simply not support the organisation of the memory module. It's totally normal that it then detects a different size. These chips are 4Mx4, the mainboard probably wants 1M, so it only detects 1/4 of the memory.
RiP wrote:And the eight 4P4256DJ-M8 chips on the Trident TVGA8900C should be 1MB but detect as 256KB 😵
Detected by what? If the Trident is jumpered for 8-bit operation, it's auto-limited to 256 KB. Also, many older sysinfo tools always show 256 KB for VGA if they can't otherwise find out (or even try) how many video RAM is present.