As John says the C class were re-engined, as such got a new lease of lease of life, redesignated B class when their 550hp engine were replaced with 1100hp (iirc).
Several of the C class were sold to NIR as the 104 class although they were not really used to their capacity by NIR.
I love the As and I'm glad for once that the silver, greens , black and BnT might be selling a little more slowly as this is my main interest and allows a little more time to gather the cash for these together. I do hope they will not be sold out on arrival and there will be enough ti hang round for a reasonable period of time so modellers can accumulate what stock they'd really like over a bit of time and potential new modelers might see them in the flesh for sale.
Personally I hope that C class are not next to come as they were far fewer than the As and looked similar to them. I'd prefer to see some variety, railcars or locos lasting fairly late in steam to provide some appeal to the masses. I even had some post-1923 grouping coaches and steam and they remain quite popular in the UK because the models merely had been available, something which has never really been possible with Irish rolling stock.