The following excerpt is from U.S. v. Floyd, 1 F.3d 867 (9th Cir. 1993):
The parol evidence rule does not preclude subsequent modifications of completely integrated agreements, however. See Shatto v. Evans, 728 F.2d 1224, 1227 n. 1 (9th Cir.1984). It appears that the district court looked to the acknowledgment's "substantial assistance" language in arriving at its "cooperation" interpretation of Floyd's obligation under the agreement. The court basically treated the acknowledgment as a modification of the original plea agreement.
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