Model M's weights at decision time are only as honest as the timestamps on every field that entered the score. This note decides which timestamp is legal for a weight decided at , and sketches lineage from vendor file to feature to weight — linking point-in-time data and corporate actions and survivorship without reteaching the full PIT contract.
Learning objectives. By the end of this note you should be able to:
- separate observation time from availability time on M's path;
- reject a weight that used a field not yet available at ;
- name survivorship failure when today's membership rebuilds history;
- attach lineage ids to the standing snapshot
pit-equity-v3@2024-06-30.
In this lesson
- The decision: what may enter ?
- Artifact: lineage sketch for M
- Limitation: rebuilt history with today's membership
- Observation time versus availability time
- Worked decision at time
- Desk checkpoint: legal timestamp
- Pitfall: path stability without time stability
- Decision card: ship weights for ?
Before you start
The full lesson, with worked examples and exercise solutions, is for members.
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