I just realized that -for the ones who don't have much time to spend on drafting- only 9 different designs would be enough to fulfill the goal.
You can do each of them 7 times in the different colors of the participants and
trara!! you have already all 63!!
This means -at least for me- I only have to sit 7 times at the sewing machine and do a batch at a time.
That's the way I plan it and I wanted to share this with you all. Perhaps it's of some help for somebody!
(Sorry, I corrected the quantity once more! mathematics are quite tricky!! thanks, Alicia for letting me know!)