I don't get this. I got to Wiki and they have a page of Irish 'tenors' with such names as Stephen Gatley (pop singer); and Daniel O' Donnell, listed as Irish tenors. I thought a tenor is specific timber of voice, and usually classically trained operatic. But able to vary the marerial so the novelty often used by record companies (Scottish Tenors/Irish Tenors) is in taking a classical delivery then applying to a totally different style of song.

So Universal Records used to market loads of those singers mixing in contemporary songs, Musical Theatre hits with standard classical repertoire. Same with Irish singers, mixing different types of songs sometimes with nationally identifiable choices.   

Although Daniel O' Donnell is an Irish crossover singer who has sung many of the same songs as Irish tenors, I find it incomprehensible that he is being labelled by Wiki as an Irish tenor. That is not anything to do with whether you like his singing or not. He has not got a classical type trained operatic voice. It depends on whether you are describing the timbre of voice, or the 'stage' genre that is conjured up by the term.

I have a song my old man wrote recorded by Daniel 'O Donnell, there is no way I would market it 'as recorded by Irish tenor' Daniel O' Donnell.   Kenneth MacKellor, Peter Morrison, Denis Clancy etc. are examples of the well known 60's and 70's Scottish Tenors. Can somebody point out any technical detail I'm missing on what makes the tenor genre?