The importance of clear dates for covers can hardly be underscored. These two are examples where the date is barely datable (if that's a word!) or not datable at all. I can date both "by association."
The first cover came in a small batch of Weddell & Co covers and pieces, all from 1936. This cover is from 1936 by association, a 2.70 pesos rate to France.
This cover is most likely from 1939 only because this specific Via Aerea postmark saw mosgt use that year. It's also a 2.70 pesos rate.