Question: How are batches created (aka "materialized")?
Answer: The batch is created/materialized only when a reviewer checks out a batch. Once it is materialized, those docs are part of the review stage even if the stage source query and other settings are modified to exclude those docs. Also, batches are family-inclusive, meaning that each batch will contain all family members within the same batch.
*IMPORTANT NOTE(Checking batches out): When you check out a batch, DISCO uses "just in time batching" which means all of the documents that may be sitting in a stage are not put into batches until the moment a reviewer requests them. This means any change in strategy in your review does not revolve around lots of deconstruction of batches that have not yet been reviewed.