There are a few cases of -ing > g/c in Munster Irish, e.g. fuilig, tarrac.
I'd assume Gaedhilg > Gaedhealaing/Gaedhiling is an example of the opposite change.

I'd love to know how the guys who made the CO chose the forms they established as standard. Sometimes they chose forms that don't exist in any living dialect. Sometimes, forms that are the least used of all the Gaeltacht forms. Looks like they chose them at random.
To me, it would have been better if they chose one living dialect as the standard and that's all. And allow all living Gaeltacht forms in all uses except in "all-Ireland" texts, ie. stuff that would be read by people from everywhere.