I spent yesterday doing the quilting on a piece that is primarily stash but the back was what I purchsed earlier this week. I am still in a Yay! mode. Picture when I get the binding on .... fingers crossed that will be later today or tomorrow.
I would not want any one to be too concerned about the exact amount of yardage that leaves the stash. It doesn't matter if you use "guesstimating" or use the width x length divided by 1440, a good general purpose calculation method. If you know you used more because of small pieces and lots of seams, then rest assured that we won't be passing judgement on the total that left your stash. We will be cheering for you and your success.
I know my February monthly "out the door" totals will be low because the two finishes that I took to the long armer won't be back until March. Rats, I had planned on them for February. Oh well, watch our March. Here I come! Any way out of the stash is.... out of the stash don't, ya know.