The loss of an Eagle was a national disgrace for the Romans. It seems unlikely that the loss of one would be unrecorded. On the other hand the fact that the legion number was not reused is suggestive of the legion being wiped out. There are at least a couple of examples where legions (and their Eagles) were lost and the legion numbers were never reused.
This is the kind of stuff that makes me wish I had become an archeologist.
Nothing stops you from being an archeologist, as a matter of fact, you may already be one. Most work of Archeology is done through research. It sounds like you are well read. Continue to read and think, at some point a question will come to your mind that you can not answer from research and you will be forced to work in the field. There are plenty of amateur archeologist out there, just become one. You don’t need a whip and a fedora to start. You have started, now get to it.
Not familiar with this particular legion, IX Hispania. Sometimes a legion would get disbanded for fighting on the losing side of a Roman civil war, or backing the wrong horse in one of the later dynastic struggles. I wonder if a new emperor might just order the name of such a legion "stricken" from all record? According to the article there are a few tidbits surviving in the Netherlands, so maybe the censors missed a few?
” There are at least a couple of examples where legions (and their Eagles) were lost and the legion numbers were never reused.”
The Battle of Teutoburg Forest, 9 AD. A confederation of Germanic tribes led by Arminius destroyed the 17th, 18th, and 19th Legions.