@dtmg27
I'm not qualified to advise formally, so please accept anything I say as the opinions of an educated layman. "National" is a direct quote from the treaty between Ireland and the UK. I take it to mean citizenship. Example: an Irish citizen, retiring to Ireland (and tax resident in Ireland), receiving a UK government service pension would pay tax on that pension only in Ireland. Conversely, a UK citizen retiring to Ireland (and tax resident in Ireland), receiving a UK government pension would pay tax on that pension only in the UK. (This second case is exactly my wife's situation). All vice versa for individuals retiring to the UK.
A quick look at the Ireland/USA DTT suggests that there is a similar provision. Look at Article 19, para 2:
"
a. Any pension paid by, or out of funds created by, a Contracting State or a political subdivision or a local authority thereof to an individual in respect of services rendered to that State or subdivision or authority shall be taxable only in that State.
b. However, such pension shall be taxable only in the other Contracting State if the individual is a resident of, and a national of, that State."
It is unhelpfully silent on the case where a pension recipient has dual citizenship/nationality. This may be at the root of the unexpected advice from your accountants. As you will be resident in Ireland
and a citizen/national of Ireland (albeit also a US citizen), they think perhaps that you fall under Article 19, 2b and not 2a for your US teaching pension.
My "clearance" was simply obtained by me writing to the Irish Revenue Commssioners in advance of our first tax return in Ireland. I spelled out our circumstances (nationality, tax residence, pension sources) and said that, after reading the DTT, my understanding was that pensions A,B,C would be taxed in the UK and pensions X,Y,Z in Ireland. Did they agree? A letter came back fairly promptly agreeing with my assumptions, and I submitted my first Form 11 income tax return accordingly.
I would suggest that you write to the Revenue Commissioners explaining your own circumstances and the advice received. Ask them how they think you should be taxed, and take it from there. In my limited experience of dealings with the Irish tax authorities, I've found them genuinely helpful (more so than HMRC in the UK and 100 times more so than in Greece where we lived just before retiring to Ireland). As a belt and braces job, perhaps send a copy of anything you do get back from Ireland to the IRS and ask for their agreement?
Good luck with it.
Paul
Edit: From Article 3 (Definitions) of the Ireland/USA DTT "i.
the term "national" in relation to a Contracting State, means any citizen of that State and any legal person, association, or other entity deriving its status as such from the laws in force in that State;"