Was there an Amazon textbook trade-in date guarantee?

I bought some textbooks on Amazon for the semester, and when I bought them I could have sworn that it said “Trade-in by December 20th to guarantee this trade in price”. I went on today and saw that the price changed, so I was curious and contacted Amazon and they claim they have no record of that.

Does anyone know if that was a real thing, or if I was just dreaming it?