Kommentar zu Bereschit 41:31

ולא יודע השבע AND THE PLENTY SHALL NOT BE KNOWN — this is the interpretation of (v. 21) “And it could not be noticed that they had eaten them up”.

This is the interpretation of “But it could not be recognized...” You might ask: [Rashi says that ולא יודע השבע is the interpretation of the good cows being eaten up.] Why did Rashi not explain that ונשכח כל השבע is the interpretation of the good cows being eaten up? Rather, he says [on v. 30] that ונשכח כל השבע is the interpretation of the ears of corn being swallowed up. The answer is: ולא נודע כי באו אל קרבנה, said of the cows in v. 21, is from the root of הודעה, and so is ולא יודע השבע here. Therefore, Rashi connects them. However, ונשכח is not from הודעה, therefore Rashi connects it with the ears being swallowed up.