Tha mi a' dol do 'n chèilidh (I am going to the ceilidh)
...but now the same show (lesson 13) is teaching me this:
Tha mi a' dol chun a' chèilidh (I am going to the ceilidh)

Aha! That concurs with my understanding of gu in other contexts as in Tha mi gu math or Tha e cairteal gu trì (up to but not beyond)
OK - the hurling of brick-bats aside - I get the idea. English would have many similar things like: "I'm going down the pub" vs "I'm going to the pub" or "I'm going round my mum's" (which doesn't mean doing doughnuts around her presumably detached dwelling). I'm content, so long as I am not missing an important nuance or grammatical point.
These are pretty different, though.
Aha! This is the danger of using material produced in the 1970s (viz. Can Seo)! I've learnt to cope with both grave and acute accents, but there's plenty of other pre-modernisation gotchas!