KFPackBuffer access to container

I am implementing a processor and I don't get the functionality of the FPackBuffer.

Its API only allows querying if a KF was notified in a specific timestamp.

Consider a KF created by a slow processor, how do we think the other processors should append their corresponding constraints to it?

I think that normally, there will be less KFpacks in the KFPackBuffer than captures in/dealt by the processor, wouldn't be useful iterating over the new KFPacks?

Am I understanding the whole think wrong?