How is that US$642.5b calculated? IIRC in 2015 we had at least two values for the dollar/pesos ratio. The official one was like 10AR$/US$, but you could buy a small amount of dollars at that value. And the street value (so called "blue dolar") was like 15AR$/US$. So which one was used? It's like a 50% difference.
(Now we had like 10 definitions of the dollar/pesos ratio. The official one is 950AR$/US$ but it's almost imposible to buy at that price. To buy dollars, the prices are around 1300AR$/US$ or 1500AR$/US$ depending on the day of the week.)
I just used the data available in Wikipedia. Instead, if we go to official data from Argentina's INDEC (national institute of statistics) we get a more reliable picture. Here [1] we see they show annual GDP (called PIB in Spanish) in constant prices of 2004 (so, they correct it by inflation). In page 6 you can see this image [2], where you see that yes, GDP hasn't really grown at all since 2011 (which is more than a decade ago). And this is aggregate GDP, but population has grown, so GDP per capita has gone down.
In 2015 the situation of the INDEC was strange, the inflation was underestimated [1] and also the dollar/peso ratio was fictional. So take all that numbers with a grain of salt. However I agree that there is (almost) no gro in the GDP in a long time. [2]
(Now we had like 10 definitions of the dollar/pesos ratio. The official one is 950AR$/US$ but it's almost imposible to buy at that price. To buy dollars, the prices are around 1300AR$/US$ or 1500AR$/US$ depending on the day of the week.)