[78-L] Letter codes on Brunswick Vocalion

[Han Enderman]

Some Vocalion labels, mainly in range 1665-1689, have a capital letter on the label,
usually after or below the cat.nr (but not a suffix).
These Vocalions are not the first pressings, but later pressings with the title in upper case.

Similar letters occur on Brunswick), below the cat.nr at 6h.
Is the meaning of such letters known?

Examples:
Voc 1634 N - Alabama Wb Stompers
Voc 1665 C - Memphis Minnie
Voc 1689 N - Alabama Wb Stompers
Br 6288 N - Ellington
Br 6292 C - Calloway
Br 6322 & 6349 C - Isham Jones
Supertone S-2087 P - Tennessee Ramblers.

Do all issues of these Isham Joneses have the letter C underneath the cat.nr?
My images of the later adjacent releases (Br 6348 Red Nichols, 6350 Lombardo, 6351 Bing Crosby)
do not show such a letter.
Note that these Br/Voc issues date from 1932.

Having written this, it seems that the letters on Br/Voc indicate the location (C = Chicago, etc.)
Additional comments welcome. It would be interesting to know the numerical range which has such letters.
The P on the Supertone must have a different (unknown) meaning.

Han Enderman