Lots get reorganized before they sell — two small lots merged into one, or one big lot rebroke into several. This field records which earlier lots fed into the current one, so you can always trace where a lot came from.
When you combine or rebreak lots, the originals are marked rebroke and the new lot keeps their IDs here. Nothing is silently deleted — the history stays intact.
Technical section
Data model, API, and internals — visible to developers.