IFRS Funded Status Question represents, practice, equation, service

segalm

The Stalla practice exam answer key says that funded status for IFRS =
GAAP Funded Status (FV Assets - PBO)
+Unrecognized Prior Service Cost
- Unrecognized Actuarial Gains
This seems odd to me. Why would the unrecognized prior service cost be added, since it represents costs that have been incurred but are not yet reflected in the PBO? It seems to me that the equation would make more sense if it were:
GAAP Funded Status (Assets - PBO)
- Unrecognized Prior Service Cost
+ Unrecognized Actuarial Gains
I’m probably making a silly mistake in my understanding, if anyone can help me it would be greatly appreciated.