Hi Rob, not trivial at all. We try to use latest OS spellings as the source for our spellings generally, so you could check there, though even then you'll get into problems (e.g. it's Sgurr Mhor on 1:25k OS maps and Sgurr Mor on 1:50k), most of your examples they have used both spellings in different scales.
I'm sure fluent Gaelic speakers can tell you many OS spellings are still incorrect, but then I guess placenames in all languages are very often corruptions of their base language and original meanings, through history. Sometimes local pronunciations are different from what a present-day Gaelic speaker would say.
An authoritative place to look is
https://www.ainmean-aite.scot/ We are trying to keep up to date with maps (and also correct typos - Mullach na Dheiragain was spelt both ways in different parts of the site, which I've now fixed). Generally the website is going to be more up to date than the book, which only gets printed very couple of years. (The Munros book is out of stock everywhere as there was a covid outbreak at the printers that shut down work in the middle of the print run. It's printing elsewhere and should be back in time for Xmas orders).