NOTATIO

Do anyone has idea why in all Make Music's music fonts there is no symbol on the keys D and d?

Hmm…, I've never notice that. Can't think of a reason why, but it doesn't apply to all MM fonts. Engraver has glyphs at both codepoints.

Right.
Sonata, Petrucci and Maestro don't have it.

In that case, it might just be an oddity carried over from Sonata to Petrucci, and from Petrucci to Maestro.

Sonata established the convention of assigning symbols to the most intuitive character slots based on similarity of shape or name (e.g. Segno in assigned to % and quarter note to q/Q). D and d might have been left empty for the sake of intuitive mapping, but I doubt it.

I doubt it too. Strange.
Keys ∆ and ∂ are mapped, though.