The perimeter advertising of Tomas Duco stadium (where the match is being held) is not from the 1970s. All the perimeter advertisements shown behind the goal line are from 2008, the year when the movie was shot.
The young Benjamín Esposito is left-handed - you can see it when he is writing some notes at the office, regarding Isidoro's letters. Old Esposito is, on the contrary, right-handed (check out the very beginning of the movie, when he's starting to write his essay).
We are to believe that Benjamin pulls on Irene's blouse, and pops off several buttons, but he didn't touch it, he missed. You can hear some buttons hit the ground, but none were actually missing from her shirt until the next shot.
In the scene where Irene and Benjamín are drinking coffee, her cup is empty. When she stirs it, you can see there is no coffee left in the spoon, yet she shakes it to drip the "pretended coffee". When she drinks, you can see the cup is empty.