Unity (iOS and Android) and loading PCKs that are built outside our player

Question

Hi, I am not an audio engineer but I've been asked to play one on TV.

In very simplified terms, I'm trying to load and play a PCK file that was built from our project but not at the same time our player was built. To be specific, we're exploring how we can deliver PCK data created by a newer player, to older players. Our old player can load the PCK but whenever I try to post an event to it, I get a '0' as the return value of the PostEvent() call, indicating that it's an invalid playing event ID.
This leads me to believe that our existing players is missing some other (perhaps pre-compiled) data that we need to also deliver, alongside the new PCK files. Does anyone know what that data might be, or if this kind of functionality is even supported by Wwise?

Thanks,
Jeff