Ah, yes I understand now what you're asking.
So with AIB a split is 2 separate contracts. There's a 'good' portion and a warehoused portion. Legally there are 2 separate loans, and AIB generally can't move amounts between the 2.
It doesn't actually matter if AIB ever expect to receive any of the warehoused amount back, as it's now a completely separate contract that just happens to be secured against the same asset. Typically there are 100% provisions against the warehoused balance as the good portion is written down to the asset value. But they have a good loan that's performing once it goes through 'curing' phase.
The customer is still legally obliged to repay the full amount.
In the case of PTSB, legally there is a single contract with a senior / junior debt part. The review clause allows PTSB to move amounts between the 2. Because it's a single contract, the entire is non-performing.
In substance, both are trying to achieve the same thing, but because of the legal contracts they are treated differently.
What PTSB have proposed is better for customers - they want to write off completely the warehoused portion. But because of the above, the remaining part would be classed as non-performing, so there's no benefit to bank.
AIB could in certain circumstances write off without impacting classification.