Yes, the server is sending per version data to the player, since armor stands do not exist on 1.7 so we have to send 1.7 specific holograms (aka horse with negative age)

Then the server is sending bad data which not would on a native client as well. Assuming the server is running 1.8, why does it even need per version data? ViaRewind should take care of entity data rewriting and emulate armor stands send by the server.

Because ViaRewind doesn't take proper care of it, it's broken. Otherwise we wouldn't do it

Then it would make more sense to report it properly, but anyway you are sending wrong data to the client. This needs fixing in your server plugins instead of ViaRewind.

The problem still persists, ViaRewind doesn't work as intended. I'm not going to fix it myself or hire a developer to do it as it's not my plugin. My commit fixes the issue immediately without breaking anything. Whether or not you want to merge this is up to you