Define MQL as a state a record enters once, on explicit criteria, with a written re-qualification window — not as a score threshold that flickers. Decide up front whether you are optimising for fast, high-recall funnel entry or precise sales-qualified handoff; the two definitions are incompatible.
The most common defect is treating MQL as a live calculation rather than a stamped event. If a record can silently un-MQL, every cohort conversion report becomes unreproducible. Stamp the date, stamp the touch that qualified it, and set an explicit window (commonly 90 days) before the same person can re-MQL.
Every claim above comes from work LeanScale published. These are the sources.