I can't put dates with the datepicker before 1-1-1970. I just discovered this when making a date of birth column and was entering some birth dates prior to 1970. I tried even with the demo on this site and the default install of mate so it must be in the code somewhere.
I did find only this post that is somewhat helpful. https://mysqlajaxtableeditor.com/discussmate/viewtopic.php?f=4&t=294&p=1119&hilit=date+before+1970&sid=28ce63880cfd2d03bbb62e43e6f339ee&sid=8f4fc93aa9963d9550a49f3cb6a0e76b#p1119