On/off switches board pinout labels

Question

I would like to know if there is a pattern to name switches board pinout, at least, for these boards.

The boards are parts of a piano toy. First one for some effects buttons and second one is the piano keyboard.

The pins are named as P10, P11,P12, P13, P20, P22, P23, P40, P43 for a 10 switches board.

At the reverse it's easy to see how switches are connected to pinout.

The reason because I ask for the labeling pattern is because I would like to connect the piano keyboard to an Arduino with Midi and, the keyboard, looks with the same labeling pattern:

Here the reverse:

Here schematic pinout for 10 switches

Answer 1

They all start with "P" other than that no obvious pattern.

they seem to be different at each end of the cable, this suggests that they are just net names allocated automatically by the design software used to design the device.