The handoff is when the client decides to stay.
You win the work in the pitch. The renewal is decided weeks later, in the early reviews, after the people who pitched have moved on.
Within days of the win, an email introduces someone the client never met. By week three, they know who they actually hired.
When I ran my own agency, I won the work and stepped away. I handed each account over the week it was signed. The renewals told me what that had cost.
The renewal decision happens in the early reviews. The client meets your second tier and quietly adjusts their expectations to match. Nothing is said. The number simply does not come back at the end of the term.
So show up after the win the way you showed up for it. The credit may come late, or not at all. The move is right regardless.
The handoff is when the client decides to stay.