I actually saw one board that held 16 Simms.
I don't recall how much memory it had, but as a repair tech I was having an argument with the owner over it.
The system kept getting memory errors with all 16 slots filled but worked fine with only 8. All the memory tested clean. Took me forever to finally agree to allow me to swap 8 higher capacities SIMMs for the 16 lower capacity SIMMs.
The one and only board I ever saw like that.