Two 1943 covers to England

I hope you can tell which one is the 1 peso on clay paper from these two covers. I will give it away further down this post. The 20c commemorative on this first cover is on clay paper.

Yes, this one. This stamp is on clay paper.

Two more 1943 Continental Grain covers

I do not see any clay stamps in this selection except for the 5c stamps on both covers.

Two 1943 Continental Grain covers

Can you tell the 20c commemorative on the first cover is clay paper?

A pair of 1942 first day covers

 It is uncommon for stamps of this issue to be honored with first day covers. The 1942 issues were some of the exceptions. Judging by the use of the selvage medallion of the 20cLC on first day covers, the 20cLC should be 1E4 since the medallion plate was especially made for this paper.

1940 Servicio Oficial cover to Sweden

 As usual, the higher values are regular issues, in this case the 1 peso stamp, and all other values are more common Servicio Oficial printings.

1939 cover to the US with 'Servicio Oficial' stamps.

 Notice that the 50c stamps are regular issues. My theory is that the higher values Servicio Oficial issues were not printed in large quantities judging by how rare they are on cover and how often regular higher values were issued instead on what, in this case, is clearly an official mailing.

1942 5 peso cover with rare censor marking

 The usual tape was not applied here, and instead only the marking "Passed by Censor" in two rows.

1942 cover to the US

 The colors on the 1 peso are consistent with the 1E4 printing on Dutch paper from 1940.