Ah I see, clever!

So in essence because the diode solution requires rows times columns diodes and this one only has a couple of parts per row and per column it scales better and for larger keyboards will end up with a substantially reduced parts count and a simpler circuit.

That patent is quite a bit younger than the synth though, so it's kind of logical that that technique would not be used, and my hunch on why they used those diodes back then is likely correct, even if we have a smarter way of doing this now.

That should work fine - the CPU would scan / energize each row independently and then check which columns are connected.

On a related note (pun intended) I once had a problem with one of these synths and its rubber contact strip. I would hit certain keys then hear a neighbor note or the same note an octave away. I thought there was a short in the scanning circuitry (I had resoldered some joints that appeared weak earlier by a ribbon connector for the keybed.)

Turns out the rubber contact strip was installed inverted. I think this one didn't have notches to make sure it was oriented correctly. After flipping it, notes sounded as expected.