Which aspect of the dream signified the fact that the plenty would not be discernable?
Rashi: It was not known that they (the fat cows) came inside them.
Verse 41:30 already said that "the plenty would be forgotten." Why does our verse say again, "the plenty will not be known"?
Malbim: Also at the time of satiation, it will not be known, because the famine is due to come, and they will prepare all 1 the grain for the years of hunger.
Ha'amek Davar: Also at the time of plenty, satiation will not be known (felt), because grain will be guarded greatly, due to fear of the hunger that will come. 2 Also refer to 41:35:152:2.
Gur Aryeh (to 41:30): The previous verse (41:30) means that any evidence of the years of plenty would fade, causing it to be forgotten - yet they might be reminded of it occasionally. This verse tells us that no trace would remain of them at all.
Presumably, he means that they will subsist minimally and save everything possible. Even if the plenty was more than twice as much as usual, perhaps they were concerned lest some spoil, or other nations will buy - both of which truly occurred (PF).
Ha'amek Davar: This is like "mi'Pnei ha'Ra'ah Ne'esaf ha'Tzadik" (Yeshayah 57:1) - due to the evil that will come.
