Patrick,
I don't have Peter Laidler's book on stock disc identification. However, quite a good source for identifying stock discs is http://www.martinihenry.com/units.htm
According ot them, Connaught Rangers have the abbreviation CT
Have you seen a picture of the disc? I suspect the person has transcribed wrongly, for example 9.14 3COR 1638 may in fact be 9.14 3CO RI 638 (Issued September 1914; 3rd Company, Royal Irish Regt, rack No 638).
The Royal Irish Regiment had a very active WW1 record - see Royal Irish Regiment - Forces War Records
This rifle has fresh shrapnel damage; I can't conceive of anything else causing that appearance. Thus it was definitely on the front line. But I reckon the report that it was owned by a dead soldier "who was still holding the carbine in his hands" is a tall story - surely it have been sent flying by the impact.
To me it looks totally honest and if I were you, I'd buy it.
Rob