Rerunning the same 20 days is not a good answer just so people can easily calculate stats.
It's not for calculating stats, it's for easy comparison.
For example, it's nice playing the same # of games, against the same competition. If I want to try some changes to my from fast to slow, I can easily directly compare the results to the other pace.
Makes sense to me. I don't see the benefit of running different days.