I looked through my cd of Nollaig from last year and the credits are also a bit confusing. Some of the songs list either Ciara or Tara, but some have no violinist listed at all. It’s also perplexing how Tara Howley is only credited on one song (The Bells of Dublin/Christmas Eve/Navan in the Snow), making it seem like she’s a special guest on the album (which she was), yet on the other side of the pamphlet it has a list of the members of cw (Mairéad, Muirġen, Caitrionas, Tara M, and Ciara) then it has the “special guest” listed as just Sibeal, and Tara Howley is credited as part of the band!
I always thought that The Bells Of Dublin/Christmas Eve/Navan In The Snow was meant to highlight Tara H rather than be the only song she's featured in, but that definitely is still weird that she only gets that one mention.
I think there are definitely some tracks that don't have a violinist. River is the one I know for certain, I remember that as being the only solo that didn't have Ciara backing at the show I went to. And I think they might have wanted to only credit the vocalists for the solos so they seemed more even. I think it's confirmed that Tara accompanied Muirgen for The Wexford Carol, but I'm uncertain about Don Oiche Ud i mBeithil (on computer). All I can say for certain is that Ciara accompanied Caitriona for the live version. I also wouldn't be surprised if Silver Bells was just the vocalists, but I can't remember how it was live and I'm too lazy to grab my CD from my room (in all fairness, I am supposed to be working

).
Also, I just now realised that there's an alternate universe where Tara Howley joins CW as a permanent member and we're left with another Lisa/Mairead situation on our hands. Tara McNeill also returns to CW in this universe for maximum confusion.