Field note
Auditing a Mixpanel implementation after a product rewrite
A product team in the Klang Valley rewrote their web app over a quarter and kept the same Mixpanel project. Historical funnels still opened. They no longer meant what the charts implied.
Event names had been preserved for “continuity”. The payloads had not. signup used to fire after email verification. It now fired when the first screen loaded. activate used to mean a completed profile. It now meant the user clicked a tooltip. Retention curves looked healthier because the definitions had become easier to satisfy.
We treated the new app as a green-field implementation. The old lexicon became a translation table, not a source of truth. Each current event was described from the code and from a recorded session, then compared with the Mixpanel lexicon and with the dashboards still on the wall.
The practical outcome was a freeze: old dashboards were marked historical, a new lexicon was published, and the first two weeks of post-rewrite data were excluded from executive views. Continuity is a choice. It is not a side effect of reusing a project ID.
If a similar mismatch is sitting on your desk, request a briefing.