Gaelic was (and still is) a predominately spoken language and very infrequently written (very few native Gaelic speakers could read or write in their native language at that time as it was not taught in schools, and its use discouraged).
The language's spellings were modernised and simplified fairly recently so the spelling in the brochure would be an old spelling.
Was just curious as my name is Eilidh and while there are many Anglicised variations of it out there I hadn't seen ceilidh like that before (apart from people not being able to say it or spell it anyway!).