While I am by no means up to knowing about these kinds of specs, my impression is this:
The main dash that's in front is like a bunch of "F#" keys. Special function keys that are pre-marked on what they are used for. In fact, Function keys have been around since the show's debut. Yet, are so useful that they're even on the keyboard in front of you, to this day. But, Function keys can't do it all. And, since they didn't have room to just whip out a QWERTY keyboard on a cord, we got these other keys that wrap about the interior. It's been hinted at that they are for general programming purposes. Still, it's near impossible to really guess as to what was suppose to do what. As has been stated before, David was probably just told to press random buttons. And, the interior just randomly alters, almost seemingly at will. Continuity on that part was pretty much a lost point from episode one, where the flashing vocal box can claim to be the Knight 2000 one minute and void of any description, the next.
So, I'm going to say that these roof buttons were apart of the A-Z & 0-9 QWERTY buttons, probably mixxing in the Timex Sinclair's programming scheme where each button meant something in BASIC.