I'm sorry to intrude, but a bunch of those are not 4-bit (although 8048 and F8 are weak CPUs).

Chess 4K Videopac: Videopac has an Intel 8048, it's 8-bit
C7010 Chess Videopac: Z80 inside module where all the chess calculations are done is 8-bit (it would be like putting Mephisto Risc in a 6502 category since the 'frontend' CPU is a 6502)
VC4000 Interton Chess II: AFAIK VC4000 has a Signetics 2560, it is 8-bit
Saba Schach, Applied Concepts Boris: Fairchild F8 is 8-bit

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CXG Sphinx Seville: Hitachi HMCS400, yup 4-bit
Excalibur King Arthur, Novag Opal II: SAM47 family? I don't know this CPU, but google says 4-bit, so Ok.