Gale!! I can totally relate to your dilemma!! It's hard to figure out the yardage for a pattern from existing stash. It always turns out that usually I don't have enough of one of the fabrics so I have to go and buy something that might match to fill in or to substitute or oneor two of my stash fabrics aren't the right 'tone/blend' to be used for the project.
LOL!! I definitely keep those fabric companies in business between what I have in my stash and my consistent buying!! It would be nice to have the right amount or the correct match up in my stash!