I agree one size* suits all in cases like this - but ask whoever negotiated the deal why not
By the time the deal was done, it was a Brexit-style 'anything for a deal' situation. It wasn't a negotiation, it was a question of, 'what will it take for SF/IRA go along with it.' They were never going to agree for a 'British Army murderers get let off' clause. In my view...
CG
* assume you meant 'rarely' to be in there?