The idea of putting a reference online with expandable spoilers makes a lot of sense - there's no reason you couldn't do that and
put just one version in the book itself.
Another unconventional technique you might consider is using something like Homeric epithets
. For example, in the Iliad, there are two characters named Aias: The first, who is really big and from Telamon, is often called something like Telamonian Aias or Giant Aias. The second is called Aias son of Oïleus, Oïlean Aias, or Locrian Aias.
While once we've learned that Telamonian Aias is big, calling him Giant Aias doesn't give any new information, it does help us remember which Aias is in this
battle scene, by giving a trait that's relevant to the action.
Other characters who don't share names are also given epithets, which help remind you who they are by linking them to their distinctive characteristics, places of origin, or relatives. So Achilles gets the epithets swift-footed, son-of-Peleus, man-breaker, lion-hearted, and godlike., while Agamemnon is son-of-Atreus and lord-of-men.
It shouldn't be to hard to use only epithets that refer to past events, not future ones.