Sadly, I was not upgraded on the way back. SeatBoost again didn't work (same error), I couldn't do OLCI because of some need to check ID at the airport, and when I asked at the check-in desk they said no, the flight was full.

FWIW, I was not treated as solicitously as on the way out in Business, and one of the attendants in Economy was downright grumpy. There was also a mix-up with the food but it was handled well (I asked for the chicken, but when I eventually took off the foil I found it was some gloop (advertised as vegetarian pasta); I complained and was told they were out of chicken; I politely but firmly said I could not eat said gloop, and to their credit the Premium Economy attendant (i.e. not the grumpy attendant) eventually produced what I think was a chicken dish from Business). And I didn't feel too bad on arrival, though I didn't manage to sleep very long/well. So I'll certainly consider Iberia again on any future trip to South America!