Yup. Kusanagi, which per the ghosts in GS is another name for Fidelacchius, is a myth that long predates the Crucifixion. I personally think that the only thing special about Ammorachius in terms of a reforging that Merlin did something to make it a far more durable container for the Sword-mantle than it had previously been able to find/manifest.
... Random thought, but I've ran down the are angels equivalent to outsiders path as well as noting the swords are vulnerable on the island and had the errant thought that the 'forging of Excalibur' in this instance could have been the release of a deity/angelic source from the island that shouldn't have been trapped there or was otherwise changed by a new host/release of Grace from host...
Huh, the British guy is the source of love lol? No, I doubt it but still, The angel/outsider connection when considering the forging came up with that^^ Also... it was the Sword of love wielder that was harmed there, someone trying to call out and wrest power from where it's been placed caused a hiccup in said power? O.o