Quote Originally Posted by DZEC View Post
Is there any discolouration on the inside of the scales? If not, then I don’t think it’s cel rot.

It is likely there was humidity trapped in the plastic wrapper and what you have is surface rust. Try using some metal cleaner like Maas, Autosol or Flitz and very fine steel wool to clean it up. If there is no pitting, it should be OK. Be careful of the edge and around the gilding on the show side of the blade.
If humidity would be the cause, how do you explain the fact there is so much more rust on one side?