If you add a new event property like "club affiliation" to your purchase events, this property will only appear on events where it is actually tracked going forward. Mixpanel does not retroactively fill in new event properties for past events by default.
However, Mixpanel offers a feature called Borrowed Properties that can help in some scenarios. With Borrowed Properties, you can "borrow" a property (such as "club affiliation") from a previous event and apply it to a later event—even if that property wasn't originally tracked on the later event. This is done at query time, not at ingestion, and works retroactively within a 7-day lookback window. For example, if a user’s "club affiliation" was tracked on a prior event (like a profile update or a login), you can configure Mixpanel to borrow that property for subsequent purchase events, allowing you to break down historical purchase events by "club affiliation"—as long as the relevant event with "club affiliation" occurred within 7 days before the purchase event.
Key points about Borrowed Properties:
- The property is borrowed from the most recent relevant event within a 7-day window before the target event.
- If no such event exists within that window, the property will be shown as (not set).
- You can create up to 20 borrowed properties per project, and only Admins/Owners can create them.
- Once set up, the borrowed property behaves like any other property in your reports and breakdowns.
So, if you want to analyze past purchase events by "club affiliation" and you have that information on a prior event within 7 days of each purchase, Borrowed Properties will enable this analysis without needing to re-track or backfill your data manually Borrowed Properties: Combine data between events on the fly | Docs: Borrowed Properties.
If "club affiliation" is not present on any prior event within the lookback window, or if you want to backfill the property for all historical events regardless of timing, you would need to update your event data in your data warehouse and re-import it into Mixpanel, which is a more involved process and not natively supported for retroactive property filling in Mixpanel.
