I understand, the owner experimented on pages 6 and 7 while leaving untouched the Roms on pages 4 and 5.

But.... once determined to ruin the cartridge, I  would have better placed a test socket on top of it....

I think the owner played burning Roms and needed a fast way to interchange them without touching the Basic Rom nor constantly opening and closing the cartridge.

You said that the cartridge memory range is the only contiguous memory zone where the original EXOS searched for Roms.