There are three versions of Professional 36 manufacture:
The first has the drained system throughs that button (as the MM Solist)
The second is that you have, has the drained system throughs screw cap (until the mid 1963)
Both version share the following characteristics; edge of the mouthpiece hole made of cork, mouthpiece like yours and part of the structure of the keys made of wood.
The third version has the edge of the mouthpiece hole made in plastic and the structure of the keys made entirely in plastic, making it lighter than two previous versions. It also incorporates the trumpet mouthpiece (such as Piano 36 ) but with narrowest internal diameter. After this appeared the Piano 36
The third is my favorite !!