L16 rom appears to be good, and I think it does work with Plymate.

Also, Franz forwarded me even more Conchess roms, from a chesscomputer collector (wieder schon danke!), coming soon:
Conchess T8, and Plymate Victoria

It's pretty clear that T8 is actually 4MHz.

*edit* I checked the library modules a bit more:
- L: on Plymate and Victoria, the CPU calls to an unexpected address and then locks up
- L16: on the Standard module, it is not detected at all
- L16: on Plymate Victoria, it get confused and messes up the board state. There's a manual available online and it says it has its own add-on cartridge (not same as for the older Plymate).