You're assuming that Ragnarok already occurred, but WoJ is that Loki is still locked up. Ergo, he's still alive, rather than being dead like he's supposed to be after Ragnarok. Everything points to Ragnarok not having occurred yet.
Again, what sources material? I haven't found many translated texts.
Many Ragnaroks have happened, or at least one I can evidence, Going back to Bob's original explanation of the queens whom used to be. They don't exist on our plain, can't anymore. Because they are primal spirits of what was, they are literally the Ghosts of a previous epoch. (You might point to the same thing for Hades and why in this age he can no longer effect fate. He admitted he could before by default then, noting a considerable difference then in how he can interact with our world now by comparison.) They birthed the new Age, also why they are now 'Mothers' despite new evidence pointing to the Queen as the one whose giving birth, they already gave birth.
Ragnarok is the end of an age and the beginning of a new one, the lifting of the veil, ect. Odin's Ragnarok happened when Valhalla fell from position on the Gates. The Jotuns retreat and reformation as Mab's court is also another point towards his story already having played out once before.... Besides, Harry killed Fenris in book 2 so no Ragnarok for you!? Unless he just freed him from the curse that contained his manifestation, Harry you dolt.
*you can find a lot of them online for free, the original Edda's even. I don't always keep track of the pages though.
**it's a poor explanation but the one were I add in the gyre and why time is repeating itself is much more complicated. The real evidence would become that it is in our mythology already.