NOTATIO

mezzo-mezzo might avoid any confusion with mezza. It's a bit wordier, but it has a nice symmetry to it. mezzo-piano, mezzo-mezzo, mezzo-forte

I tend to think of all dynamics as being varying degrees of either piano or forte. Mezzo is as much a qualifier as --issimo.

One can speak loudly, or softly, or somewhat loudly, or somewhat softly etc.

But one can also speak in a "normal conversational level, which Google AI just informed me as at about 60-70 Db or interestingly right around the middle range of 64 Db that ehellner suggested.

I have often been torn as to how to notate such a dynamic. mf or mp? I usually settle on mf as suggested by RMK, but am rarely happy about It and welcome the new choice of mezzo or whatever one calls it.

mezzo-mezzo seems cumbersome and takes up so much space. What about Mezzo with a capital M and mz for short.

RMK, I am sorry that I haven't answered your two questions directly. I think I have described what I consider a "neutral dynamic". And concerning mf and Beethoven, to the best of my knowledge which is largely limited to the piano rep., he used very few mf 's, nor did Mozart, with the same limitation.

I just look through several works of Chopin and found several pieces in which there is no dynamic indication at the beginning or at important junctures later in the piece. These instances seem to indicate a neutral dynamic. This is not the case with Mozart, who sometimes omitted an initial f or p when he felt it was obvious because of the dynamics that follow.