I'm looking through course material from Source Selection taught by Management Concepts and they have the following definitions for "Marginal" and "Unacceptable."
Marginal - Fails to meet minimum evaluation standards; low probability of satisfying the requirement; has significant deficiencies, but they are correctable.
Unacceptable - Fails to meet a minimum requirement; deficiency requires a major revision to the proposal to make it correct.
This goes against everything I thought I knew. Has anyone ever rated a proposal that had "significant deficiencies" anything other than unacceptable?