That's supposedly WAD. The Welsh have generic ideas in EU4, so the converter doesn't have any ideas to assign to them. Same for cultures like Armenian or Georgian. But cultures like Berber and Bedouin have defined cultural ideas - they end up getting generic ideas on conversion is clearly not WAD.Do the welsh still not get ideas because I know the last time I exported a game which was a while back and all my welsh kingdom got was the Generic national ideas.
I'm currently trying to verify if what you found in the files somehow messes up the conversion. For example, Kurdish is listed twice in the culture group list for some reason.Ibadi and Miaphysite are in heresy_table_soa in addition to religion_table. So I guess the mapping in heresy_table overrides the one in religion_table.
Still though they should be removed from heresy_table (because they don't belong there) and the value in religion_table should be corrected.
EDIT: Added the issues that definitively cropped up ingame to the list.