This area is one where the regulations change and where much depends on the customs officials on the day, regardless of what the official policy is.
The entry to Ecuador is a classic case - what the actual regulations have been for the last couple of years is uncertain - the reality is that a number of travellers got in without a carnet, (with significant LOCAL help) and several more were completely unsuccessful. At least one had to wait 10 days for a carnet to be issued at home and couriered out before he could clear his bike. A few days later someone got in without a carnet.
It seems clear NOW that FLYING into Ecuador the CURRENT regulations DO require a carnet - this has changed very recently. A carnetless traveller was recently required to ride to the Peruvian border with a Customs officer on the back of the bike, and pay for all his expenses, including his return to the airport.
As for Argentina - it may help that you are Argentinean!
And speak the language. There has been another recent report of hassle without a carnet into Argentina.
That you were never asked for a carnet is interesting - when we arrived there from South Africa by air, they wanted an Argentinean to guarantee
the entry. It took hours to sort it out. They never mentioned a temporary permit, and eventually we used our carnet.
Seems like a little of the Ecuador situation - different officials have their own ideas about what is required. They just didn't seem to want to let us in without a lot of aggro, and there have been a number of other similar reports.
However, your information is very useful for future travellers - now they KNOW the name of the document required, that should get problems sorted.
Thanks for pointing that out.
Seek, and ye shall find.
One world, Two wheels.