Now, I am only saying it's a possibility that there is an issue with trying to link the old Ratatoskr with the new one- we have seen problems with this before where someone claimed if they locked something away, the new ability user wouldn't be able to unlock it.
That "rule" could also just simply not apply to Ratatoskr too so you don't have to get worked up. It's possible any version of him can unfreeze stuff, but I'm pointing out that since there are two different creatures then there is the possibility they each have their own authority over the ability.
If that's true, then anything the old Ratatoskr froze centuries ago before it turned into the hammer can't be unfrozen by the new one, now.
Note: It's a good theory, that the Galley La giants were preserved by the original Ratatoskr, but we shouldn't operate on the assumption that just because Xebec wanted the Nika fruit, the Niddhogger fruit, and the Galley La giants, that it means Ragnir froze them. Any number of things could've happened to them, and their resolution may not involve Ragnir at all. It could, but it's not certain yet.
