Teaser 2948: A hardy annual

From The Sunday Times, 24th March 2019 [link]

Yesterday was my grandson’s birthday and we continued a family tradition. I asked him to use any eight different non-zero digits (once each) to form a set of numbers that added to 2019. Last year I asked the equivalent question with a sum of 2018, and I have done this each year for over ten years. Only on one occasion has he been unable to complete the task.

In this year’s answer his set of numbers included a 3-figure prime that had also featured in last year’s numbers.

(a) In which year was he unable to complete the task?

(b) What was the 3-figure prime that featured in this year’s answer?