It's difficult to say which market the dual-format games are aimed at.
The Electron is effectively a cut-down BBC microcomputer, it would be like Sega releasing the Genesis then later removing and downgrading components and releasing the resultant Master System (or equivalent).
The BBC Micro was aimed as being an educational machine and had high specs which priced it out the range of many households, so to compete with the likes of the ZX Spectrum the cut-down Electron was released as a games and general purpose machine. I'm no expert, but I suspect the dual format games were originally designed for the BBC and then rendered more simplistic for the Electron, though they could be created independently.
Currently Electron is listed as a sub-category of BBC, I would propose rolling with that and listing dual-format games as being BBC and noting Electron in the notes as you suggest. Does that sound good?