I guess but if we look at Ae Fond Kiss for example. Many release state trad despite it being a Robert Burns song. https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=6&cad=rja&uact=8&ved=0ahUKEwjLlsKUwOnTAhWJLcAKHarvBVsQFgg_MAU&url=http%3A%2F%2Fwww.rampantscotland.com%2Fsongs%2Fblsongs_kiss.htm&usg=AFQjCNGijdlGD77Bw71wzaHdtwWM5AYDCA&sig2=b1qfTpyHdqOjGf6GxAk6uQ is one example. tunearch.org/wiki/Ae_Fond_Kiss
One Discogs entry https://www.discogs.com/release/3678135-Ae-Fond-Kiss/images
Another entry https://www.discogs.com/Anne-Lorne-Gillies-Milestone/release/6104094
What do we do if a release says trad, but we know it's written by Robert Burns. Many trad songs despite the writer being know is credited as trad.
Massacre Of Glencoe being one such example is often credited as trad despite it being written by Jim McLean.
I'm not saying you are wrong. But if the writer is known; but it states trad ie on a vinyl, then should the orginal credit be added.