Originally Posted by
TravellingSalesman
OP should have a back-up car seat at home?
Recently experienced the same scenario on AC at La Guardia. Very different outcome, they gave us a spare car seat (sourced from another airline as they had given all of their own away).
AC at LGA isn’t a home destination though is it.
The Montreal Convention on international flights covers an airlines obligations. They rarely go above and beyond that and follow the rules directly.