How could having more US dollars solidified the 1991 Argentine peg to the US dollar?
Simply having more dollars may have served two purposes. Firstly, more dollars would mean that the central bank could have bought more pesos and exerted some upward pressure on the exchange rate. Secondly, fixed exchange rates can fall because of expectations about the central bank's credibility to its peg. If the prevailing expectation is that the central bank does not have the resources (reserves) or the will to defend the peg, pesos will begin to be sold en masse in the expectation of a devaluation.