The problem
Sent means WhatsApp's servers took the message; delivered means it reached the recipient's phone or one of their linked devices; read means WhatsApp reported that the recipient read it.
For the cases where a tick is missing or misleading, see why WhatsApp read receipts lie to your dashboard.
Design the boundary
Keep each transition in an append-only event log and apply monotonic ordering when events arrive late.
Process the interaction
Do not infer order fulfillment, consent or task completion from a read receipt.
Measure the outcome
Measure state transition latency and unknown or failed outcomes separately.