1941 Argentina Backstamps

I'm in the process of updating my FDC exhibit of the 1941 3c Vermont Statehood stamp (March 4, 1941).

Currently working on FDC used to foreign destinations. Two of my FDCs are to Argentina. Each of the covers has a single stamp paying the correct postage rate which was in effect from April 1, 1932 to November 1, 1953.

On the reverse of each cover are the circular handstamps shown in the illustration. Is any one able to tell me the significance of round handstamps? Thanks in advance.

Looks like some type of censor marking.

Nothing in my records.
All I can suggest is perhaps a link to "SUC" = Surcusal.
Surcusal
SUCURSAL: Branch (Office) (Usually with indication of Railway or route). Sucursal Nos. 2,4, 5, 8, & 37 were TPOs.

Good Luck

I was thinking it odd, that any remnant of this auxilliary marking
does not show up in my 50 or so covers, or 1,500 stamps.
Searching was becoming fruitless.

I was thinking maybe an image of the front of a cover may give us a clue,
then, with text string "Argentina Backstamps"
This popped up.......... 23/55 ?

In both cases the numeral in the top ring segment, coincides with the Argentine branch

https://victorgg.com/item/new-zeala...-s-hororata/


Received Buenos Aires Circular 23/45

In this case, it agrees with Perf 12 suggestion.
the (Unsplit) ring, appears to coincide with the Censor seal number.

https://www.ebay.com/itm/1942-SCOTT...333288845286