Going with what McMillan said, for a long time Scots didn't have standardized spelling. In fact, most of the time it's wasn't written at all. Except on a few occasions (Robert Burns) it was exclusively spoken language. That is what makes it so difficult to write. Nowadays, the Ulster-Scots Agency (Tha Boord O' Ulster-Scots) is working to standardize the spelling, but it's still a good ways away.