I tried to redo the same booking.
In the summary of fare condition, it does state that the return must be done 1 year after my departure date.

In the detailed fare conditions, it gives me a different fare basis than ASUM1Y, it is A1YIBPT:

1 - PSGR P1 ADT RULES DISPLAY
FARE COMPONENT 1 ADT PARKUL CX A1YIBPT PU 1 N
FCL: A1YIBPT TRF: 170 RULE: F510 BK: A
PTC: ADT-ADULT FTC: FR -FIRST CLASS RESTRICTED

There is nowhere here (maybe I missed it) where the validity is indicated. But the summary says return is valid for one year from departure.