There is a large section on the Irish factor in the army organisation in pages 45 to 57 of Houlding's "Fit for Service" but I must admit it is mainly discussing the situation in the late 18th Century. It does say that there were 27 infantry regiments based in Ireland in the 1790s compared to an average of 16 in mainland Britain but there were actually less troops in Ireland. Houlding does not however list them by regimental number.
Could it simply be that each time a tranche of increases (such as raising of a number of second battalions) was authorised there was a conflict between what the army wanted and what the treasury would pay for and the resolution produced different figures each time. In a typically British pragmatic way there was no general attempt to retrospectively amend previously authorised establishments. These apparent varaitions in establishment would not be of much significance since relatively few battalions were recruited to their full authorised complement.