We have had a few occasions where a solicitation or verbal pledge for a donor has been blended between two proposals, or a donor simultaneously ends / declines one proposal and leaves an opening for a new one.
In addition to using proposals to track our moves management and solicitation actions, we also use them to track our projections to certain funds & purposes; thus, it's important the funds/purposes expected amounts remain separate but the actions can overlap.
I run into this all the time with grants - many meetings address current funding as well as upcoming opportunities/renewals, with much of the information co-mingled/relevant to both opportunities.