Scouter, You may notice that much of the mail from the Central and South American countries is to Large companies in the U.S.,Canada, Germany etc...they needed letters to arrive on a timely basis..if they went by boat it could take months for mail to arrive...much of the mail service from those areas is still spotty !!
We send Christmas cards in September to make sure they get to Colombia in time. It seems mail to Colombia was quicker in the 20's and 30,s (so I am told) and that went by steamship to probably Barranquilla, plane down the Magdalena River and probably burro up to Bogota. It was also cheaper.
Mail to/from Colombia is notorious..., I would never ship anything of value by mail to Colombia. And indeed, in the 20th with SCADTA/Lansa and later on Avianca it had been much faster and more reliable as today.
i remember shortly after I joinned the Guatemala stamp society..Guatemala hired Canada Post to straighten out their mail problem...it was said piles of mail would sit for months at the Guatemala City post office !!