Just to muddy the water some:
We crossed back into Argentina at Paso Roballos on Jan 18 and did not have to show proof of paying the reciprocity fee.
In fact, they didn't even have a computer, so scanning a document was out of the question. At some point this will all change, but for now, if you needed a way into Argentina, Paso Roballos is worth a shot. And if it were me, I would bring a nice looking version of the document that DRRambler was kind enough to post in case they do start asking for proof...