Diameters of congaheads - When did congaheads get their zise?

[Sonorito]

This is the diameters (or size) of the drumheads on the Session Line congas of PJ Percussion of Denmark:

Quinto width 11'' = 27,9 cm
Conga width 11 3/4'' = 29,8 cm
Tumba width. 12 1/2'' = 31,8 cm
Tumba XLwidth. 13'' = 33,0 cm

The reason why i write this is the following question which has started to nag me: When did the heads of congadrums get their current standarised dimensions?

I have looked at pictures of congas from the fifties and sixties (mainly gleaned from record covers) and to me it seems the diameters of the heads vary wildly, and the heights of the drums too. There are different ways of attaching the skin from nailing to rather "primitive" hardware with a likeness approaching what we are used to see today. (And for all I know maybe glue has been used in some instances.)

And another thing when i listen to those records: Have "modern" congas and bongos been tuned up? These older recordings have less of sharp diskant-tones, and some time the sounds seem to be more "muddled" or shall i say; not so clearly defined in pitch.

Another place in the world to ask this question I don't know of, so this is the reason why I bother you with it.

@age