Thank you, Pagoda. Your input is valuable. Now I can mount this cover on a page with correct information. The "label" of the Mexico PO is actually an officially seal label. Letter was opened in attempt to find the sender. During the Mexico revolution, there were lots undeliverable letters that were treated this was. Mexico was in a civil war. Many POs were closed "for business". This particular mail actually was returned to the sender, because it does not have "Advertized" nor "dead letter" office cancellation. This is a real postal history!
Here is a tipical letter that went to the "dead letterr"department of the PO. It was advertized (LISTA), unclaimed (NO RECLAMADO) and the dead letter office (REZAGOS) handstamp.

