if you know Durcan, Yeats and Ni Chuilleanain are you safe because they are the only Irish poets on the course this year and there has to be at least one irish poet on every year?
There doesn't have to be any trend i'd advise knowing 5 just to be safe
Personally, I have only studied the three Irish poets and also Plath just to give me one more option.
They rarely change their habits, I wouldn't be too worried about the trend failing us.
What about Durcan and Bishop only and Larkin a bit would I be safe