Mortgage Interest Relief amounts constantly varying

I have been examining my mortgage over the past couple of nights and have a query that I hope some knowledgable AAM'ers can help with.

We are in Year 11 (first payment was January 2002) of our mortgage and therefore mortgage interest relief is well finished. However, going back over the monthly schedule of repayments, the monthly amount of mortgage interest relief that was dealt with at source by the bank varied from month to month and year to year. Our monthly outgoing was made up of repayment+overpayment+MIR to give a constant total which has never changed. When I say vary,

What variables would have affected the MIR repayments? I know that there is descending relief through the seven years and obviously interest rate changes but is there anything else? The MIR would vary from month to month, sometimes by a couple of euro. During all of this time, our overpayment remained constant as did our overall total monthly outgoing.

Glad for some help on this. I have tried to find the historical MIR rates but they don't seem to be on the Revenue website.

I think MIR is calculated on the full annual amount of interest paid not the monthly amount of interest you pay every month. You pay a different amount of interest every month so id say your MIR changes every month to keep your repayments constant

Apologies for bringing this back up again, but I have been doing some further number crunching on our mortgage.

In terms of Mortgage Interest Relief, I have calculated that the bank calculated TRS at 14.5% the first year (I think due to them not deducting until month 4 of the year), then 20% for the next five years, then 15% and finally 8.5% for the first three months of the last year.

Does this look and sound right to others? I have tried to find the historical TRS rates for a house bought in 2001, but can't. When I work out the difference if the bank had calculated the full TRS in year one compared to the piecemeal approach they adopted, the difference is approx. €150. Is it worth going after them for that?