I bought my mare’s saddle when she was a 3 year old. It fit her like a glove.
As a six year old who decided to develop some muscle, not so much; the saddle pinches a bit behind her shoulders, which tips the saddle forward (the skirt in the back is about 3/4" off her back.) It’s not the worst fit in the world, but it’s obviously tight behind her shoulder area.
I come from the school of thought that pads won’t fix an ill-fitting saddle, but when I’ve lamented to friends about having to buy a new saddle, every single one—even experienced horsemen whose judgement I trust—have responded with, “Why don’t you just get a corrective pad?”
Did I miss the memo on the magical abilities of corrective pads? Should I really try that route before saddle hunting again?