This is the best answer here and it helped me. Using this, I was able to get a working version that prefills all contacts with a value.
I’ll provide my code here. Maybe the context will help someone else.
First it checks to make sure the fields exist. If either one is missing, the formula returns “no” and that is updated o nthe contact record. If they both exist, the formula proceeds to evaluating if one date is greater than (after) the other.
if (
is_known( date1 ),
if(
is_known( date2 ),
if(
date1 > date2,
“Yes”,
“No”
),
“No”
),
“No”
)
We had to do this because you cannot filter based on one date property being before or after another date property. So this calculation allows us to select it in report filtering. An absurd work around, but it works.