You need to look at the Reference Images previous to your batch image. At the top of your page, you'll see that it is "sheet #4." Use the 4th vertical icon to show the Reference Images. Likely at reference image -3, you'll find the first page of the Roster your page is a part of, and it should have a date that you can use. Very likely, it will say June 30, 1919. You are allowed to use that Monthly Roster date for all the names on your sheet because they don't have individual enlistment dates. The Roster or Roll date is the next best Military Date to use in that situation - per the Military Date Field Help (purple question mark).