Two 1942 covers to the U.S. via Trinidad.

 Both of these covers have a clear Trinidad mark, and we can see that the only letters on this mark are TRI and IC. Both of these are common 1.15 pesos rates with 1 peso and 15cSC stamps.

A few more Continental Grain covers

 These are from 1942. Both have Miami, FL transit marks.

The 30c stamp has a plate variety.

A few Continental Grain covers

 These are from 1942-3. All have Miami, FL transit marks.

1942 cover to the U.S. with Trinidad transit

 Trinidad was used as a transit location in 1942. 

Interesting that the 6c was used instead of the 5c. The cover has a 1c over pay. 

The Trinidad transit mark only has so many letters (this is the complete and fully legible marking). The mark only has the letters TRI and IC. 

Three 1942 covers bearing 5c and 10c stamps

This first cover was mailed within Buenos Aires city, and the slogan reads: "(quoting Estrada): Libertad is an indigenous American plant."

The slogan reads: "Phonograph record mail service to domiciles, call the phone number Retiro 6339." Addressed to the Reader's Digest (U.S.)

Addressed to the Reader's Digest (U.S.)

1942 Local Express cover

 Sent from Lujan to Buenos Aires.

Two 'cents' 1942 ship covers

This first cover was sent to the US with the request "Send only by the first Argentinean ship to the U.S.," and instead of bearing a 15cSC, it bears a combination of the 12c and 3c stamps. The 12c stamp is always rare on cover. 

The slogan reads: "Use airmail for out of country."

This cover to Colombia has a "passed by censor" mark that was most likely applied upon receipt."