Hi SpiritFox,
1) You don't need to add following block, i had added it just to insert some entries into the table for demo.
It will work without this :)

2) I think it is a bug; when I select the "custom" option I can't search the days before today. If you select another option and go back to "custom" it already gives
- Verify in your screenshot that you have December 2019 month calendar opened on the left and by default it is not allowing to select date before 31Dec2019. In this case, you can set a minimum date in 'MinDate' property of Date Picker as showed in below picture to allow the user to select dates from a defined MinDate.

You can select dates before today in 2020 calender using '>' this icon.
Thanks, Happy Learning :)