In December 2013 and January 2014 I did a couple of flights with Aerolineas Argentinas. Since some of them would let me earn a lot of miles, I'd like to join a loyalty program where I'll get miles for the flights.
Aerolineas Argentinas is member of Skyteam. Each of the member airline has its own loyalty program. Currently, out of these loyalty programs, I'm only member of Flying Blue. However, Flying Blue requires the original boarding documents which I don't have anymore. I tried to join Aerolineas Plus to get my miles there, but they require that you already have been a member at the time of the flights.
So my question is: Which loyalty program can/should I choose so that I still can get miles for these flights?