Agreed with AKM Sama. Also, the existence of "Anime only characters" has no relevance about a series canon; it's more about the context. Gregory is a minor character whose existence neither contributes nor contradicts anything regarding plot. So him appearing in Super doesn't make Super non-canon nor does it make the Anime canon. Filler doesn't automatically make it non-canon; filler that's often added in Manga to Anime adaptations is usually non canon, but even original canon manga can have content described as "Filler". Filler is just a fancy word for side quest, which Copy Vegeta may not be important to plot, but he's still technically part of the canon. "Filler has often been used for RPGs where you have to do certain tasks before you can get into the main quest.
Also, Bardock isn't the best example; he was always a canon character, we just don't know much about his story in the original manga. But the Broly movie recently made it and it differs greatly from the Toei Verse version. Tarble is now technically a canon character given his recent mention, but "Yo Son Goku and his Friends Return" is not. Bardock's gang are also canon characters now, but it's just we only recently met the canon incarnations. I recall they've yet to actually meet him as far as Super and the Broly movie are concerned.
And that's not at all the sole reason GT is non-canon to the original Manga. GT is non-canon for many reasons, but is a canon sequel to the original DBZ Anime. And the primary reason why it's non-canon now is Toriyama himself confirming it's non-canon. I forgot where the article was, but there was an article explaining the Anime adaptations, movies, and GT are all part of an alternate continuity made back in 2013. GT is called "The Grand Story side" due to it being considered the most important non-canon work. "Story side", "alternate reality", or "parallel universe" are all common TV Tropes of an author calling a work non-canon. And it's not solely because of Cooler appearing in GT, but rather many other movie and filler characters appearing in other movies and fillers throughout the Animation. And the Z Fighters outright recognizing them defeated villains.
It's different in Super's case, when ever a character who was originally Anime only appears, they appear to be either on the sidelines not referencing any incidents from the Anime. Or are introduced as new characters. There's also a big difference between non-canon characters and non-canon versions of canon characters. Super is the primary canon regardless of Anime or Manga; but their are two canons technically speaking. The two movies BoG and RoF are non-canon and neither are GT or Kai.