Except that they're teaching us the Gaelic spelling of the vocative case - so not really a case of 'anything goes'.
There are many ways to spell Neil, and using the original must be as good as any.
Why is it "a Neill" here, but earlier I saw "Greas ort, Fhionnlaigh" with no "a"??
Because Fhionnlaigh begins with a vowel sound since "Fh" is silent. So you don't use the initial a.
Too clever for me all this slenderising and stuff. I'll just have to go with the flow. As long as i can speak it and read it i will be cho toilichte