No secondtimearound - you aren't short changing yourself. You would though if your Tuesday/Wednesday family wanted to come Monday instead of paying you for the stat day, that is what is happening with the others. Parents will just move their days around to avoid paying for a stat day because how terrible is it that they have to pay for a day their child is not attending!
My way of avoiding the whole issue is by charging all part-time kids for stats no matter what day the stat falls on. I will have 2 part-time kids come September. They will both be charged for the stat days no matter what.