Picture a B2B software company running paid search with a 90-day sales cycle, where only about one demo request in twenty closes. Google Ads only sees the form fill, so Smart Bidding keeps going after the cheapest demo requests, and those often come from the wrong people. Offline conversion import is the usual fix, but you still have to pick which event to send back.
Sending every stage (MQL, SQL, opportunity) gives the bidder more volume to learn from, but each stage is judged by a different person in sales, so the signal gets noisy. Sending only closed-won is cleaner, but it can take months to collect enough wins for the algorithm to change anything.
My view is to import a qualified stage like SQL early, then move to closed-won once you have a steady number of wins each month. Which stage are you feeding back, and how long did it take before the bidding actually shifted?