Yeah. the early celts (Example: the Gauls and possibly Picts) had little in common with the medieval Irish.
Celts from Spain ['celtiberians'] colonized Ireland and named it after one of their Goddesses [eriu]. They then several centuries later colonized Scotland, Iceland, Man, etc.
Unfortunately, the Welsh, Bretons, and Cornish are not among these, so they're very distant cousins.
That's why the Celtic civ is too broad to work for the modern era. It's like having a Slavic civ and using Rurik and Stalin.