Hello bluezyboy, welcome to the Forums!
You're not the only one with this issue. A repeating pattern for many people is that Artifacts obtained from
fishing will not count towards the collection. Despite this, you
should still be able to get the "A Complete Collection" achievement (and quite likely
Perfection), even though it isn't "filled in" in your collection screen.
A potential work-around for the issue is to get the artifact from a source other than fishing. Since the Ancient Sword can be obtained through Artifact Troves (
wiki link), I would recommend using those if you want to try and fix the issue!
Hope this helps!