I started using a tub of Cella, that was opened maybe 5-6 years ago, found it in the back of my soap cabinet, and thought it was a new tub.
I flooded with water and let it set over night, poured the water off in the morning and been using it for a couple weeks now, just fine. I do the same with MWF.
The color of the soap, is a little more yellow than I remember, but it smells and lathers just fine. I had forgotten what a good soap it is.