If by donor you mean patron -- I have the impression that a large part of this community also is patron to DC. I am myself.
And to your "theory" about the game always coming out the day after end of month...
0.20.0: finished 99% as of April 29th 2020 (main story)
0.19.5: December 20th 2019 (Consuela) -> 2 months
0.19.1: October 19th 2019 (Eve) -> 4.5 months
0.18.5: June 4th 2019 (Jenny 2) -> 1 month
0.18.0: May 2nd 2019 (Jenny) -> 4.5 months
0.17.5: Dec 16th 2018 (Daisy) -> 1- month
0.17.0: Nov 23rd 2018 (Diane) -> 4 months
0.16.0: July 25th 2018 (Roxxy) -> 3+ months
0.15.1: April 15th 2018 (teachers) -> 4 months
0.14.5: December 19th 2017 (Debbie) -> 1.5 months
0.14.3: November 1st 2017 (Aqua) -> 0.5 months
0.14: October 13th 2017 (Mia) -> 2- months
0.13: August 21st 2017 (Erik)
This means it you are right two times out of 12. Three if you count June 4th 2019 as well. Congratulations.
In this list you also see that they do not slow down releasing stuff. This release is a bit late, admitted, but they also claim it's a large update.