starter blow off

Well I was trying to plan ahead and stepped up a yeast starter a second time to save for my next brewing day. I woke up and found a huge mess of dried sticky yeast all over the counter. I lost approximately 100-200 ml of volume in the container. I used a yeast calculator to determine how much yeast I should have had. Am I safe to use a ratio of what I should have had to what I currently have for an estimate of yeast cells remaining. I am using a stir plate, and had checked on the starter at 18 hours with no issues.