“Then they can boost older content from the hosting site.” No that’s the problem. Like you yourself said back catalogues arent fetched. They can’t see the older content to be able to boost it, they’ll only see new content.
If my instance follows a community at time t = T, and your instance starts following it at time t = T+10, I can boost content posted between T and T+9 so that you can see it.
Meanwhile, if people on the hosting instance boost things posted from times earlier than T, we both get to see them. Then, once they’re visible to us, we can continue to boost them for new instances to see.
“Then they can boost older content from the hosting site.” No that’s the problem. Like you yourself said back catalogues arent fetched. They can’t see the older content to be able to boost it, they’ll only see new content.
If my instance follows a community at time t = T, and your instance starts following it at time t = T+10, I can boost content posted between T and T+9 so that you can see it.
Meanwhile, if people on the hosting instance boost things posted from times earlier than T, we both get to see them. Then, once they’re visible to us, we can continue to boost them for new instances to see.