They say the differences in settings came about from musicians adapting tunes to suit their instruments, as well as just forgetting or incorrectly hearing a tune. It’s one thing that gives Irish music its great diversity. I’ve made up settings of fiddle tunes that I took a liking to, such as their version of Jennie’s Welcome. Lots of fun to be had! They’ve some really great tunes.
Also, notice the difference between the original Scottish settings of tunes and what they became when they came to Ireland. The Caber Feidh turning into Rakish Paddy is the one I always think of. Caber Feidh starts on a low C. Some piper wanted to learn that tune, so he started it off on his middle C instead, changing its character a great deal in the process. Does anyone miss that low C anymore? Trying to follow the original Scottish setting on the middle C, jumping down to low E, sounds unnatural and contrived.