A plan, a portfolio, a benefit case and a reporting cadence — none of which you built. The plan encodes assumptions nobody has revisited. The benefit case was written to get funded, not to be defended. And the reporting was designed to show progress, not to answer whether the enterprise changed.
Once you have presented the inherited numbers to a board, they become yours. Every quarter you carry them without testing them is a quarter of your own credibility attached to a claim you have not verified.
Not the plan. The work population underneath it: what enters, who admitted it, what evidence exists, and whether the benefit case can be reconciled to anything. That read takes days, not a quarter — and it is the only thing that lets you re-baseline honestly rather than defensively.