Earlier this year I was thinking about doing a early May Magic cruise. I watched the guarantee rates and they did drop further so I ended up booking it. I was glad I did at the time because shortly after the guarantee rates went back up a couple hundred. I met a a Disney World CM on the cruise who I talked with quite a bit. I mentioned what I paid, and she didn't tell me how much she paid with her discount, but she said it was more than what I paid.
But I don't think that this happens a lot. The cruise I was on was definitely not sold out.