How to make textjoin a drop down box instead?

[DigitalZugzwang]

First off, I have found this board very helpful and want to thank everyone for that. I also thank you in advance for help with this new issue.

So in order to keep our Work In Progess (WIP) tracking accurate, I'm having the users record activities. These activities are dated by the user and the date of the entry is also kept. The idea is to allow a user to pick either today's date or a previous entry date. By picking today's date a new activity is recorded but picking a previous date, the older related activity would be replace in the table. Now to get to this point I first would like to limit the user's options so mistaken dates aren't entered.

=TEXTJOIN(", ",1,TEXT(IF(FREQUENCY(IF(WIPTrack[Job]='WIP Update'!$B$8,IF(WIPTrack[Bid]='WIP Update'!$B$9,MATCH(WIPTrack[Update],WIPTrack[Update],0))),ROW(WIPTrack[Update])-MIN(ROW(WIPTrack[Update]))+1),WIPTrack[Update],""),"mm/dd/yy"))

Above is a formula that will list all the relevant entry dates in the same cell. However, this would still require the user to enter a date. I would like to make it a drop down box, with today's date as the first option. I can't seem to figure out how to turn the above formula into a data validation list.

Again thank you for your help.

 

[DigitalZugzwang]

Doesn't anyone know how to create a drop down list based on two user entered values extracted from a table while adding the Today() function? Or how to take the result from the formula above and change it to a drop down list (while also adding the Today () function?

Any help would be very appreciated.