Ok, I think I now see the source of the confusion.
An accrued-to-date liability refers to the present day value of pension liabilities, ignoring any liabilities that may arise as a result of future service, etc. In other words, it's a snap-shot of the State's accrued pension liabilities today.
Basically, it's the capitalised value of the projected benefits (future cash outflows), applying an appropriate discount rate. A wide range of actuarial assumptions are obviously embedded in the calculation.
Put another way, if I say the accrued-to-date pension liabilities of the State to (current, deferred and retired) public servants are ~€115bn (or whatever), that is an actuarial estimate of what those liabilities will ultimately cost the State (expressed in 2018 money terms).
So, if those liabilities were crystallised and settled today, that would obviously cost the State ~€115bn.
Hopefully we can agree that would not be realistic.