Teribus, the Officials have not actually disarmed at all. They have been on a kind of ceasefire since the 1970s and it's assumed they are no longer active. Yet it was Provo weapons that were decommissioned.
Also, regarding numbers, the various republican militant groups - Provisional, Official, INLA, etc., were responsible for around 1,950 of the 3,500 or so deaths during the Troubles. Loyalist militants were responsible for about 800 with the remainder divided between the RUC (Northern Police Force) and the British Army. The Irish army and police contributed neglible numbers.
The Real IRA (a splinter group from the Provos which didn't agree with the 1998 agreement) claimed responsibility for the Omagh bomb. Thankfully the British didn't regard this bombing as "a bombing by an Irish terrorist group" and decide to bomb the southern half of the country into a car park (thanks guys, BTW).