Two sites that helped immensely with the RegEx I utilized (not sure why I bothered with spoiler tags three years later, but so be it):
This page helps a lot with dates:
Hello there @dataMack
Here my second take on this solution. I submitted my first one in 2017.
Without taking a peak at the other's solutions, I knew that it could be done to use one single REGEX tool to extract the 6 different date formats in this weekly challenge. Once all those date formats have been extracted, the approach is to create a null date field and start date parsing the matched formats; thus, you can see that if a date parse has been executed by matching it, the following attempts are not executed because the date field would not be null anymore.
The approach to extracting the 6 different date formats has to be from longest to shortest; we would first need to identify and define a DD-MM-YYYY before a D-MM-YY in the REGEX tool; the formula date parsing would work on a similar fashion; it would first parse the longest matches before parsing the shortest matches.
I am comfortable enough with regular expressions to turn to them to solve the thorniest of string manipulation problems. However, I always use the RegEx tool's expression builder with the dropdown to remind me of the syntax. Parts of this are kinda ugly because I got stuck trying to do too many things with one expression.