Recording a possible person

How do you normally record a person who may or may not have existed ?

For example, I have heard of a particular part of the family who had children called Brian, Mary, Joe & possibly a fourth called David.

I can certainly enter in an individual called David, but I don't want him to go down on the record as officially existing until I have some way of verifying it. At the same time I don't want to not record him in case I forget to come back and follow up.

I could obviously add him and put in a note "may or may not have existed", but I'm wondering is there a standard that is normally followed along the lines of "around 1900" being an allowable date.

z

p.s. I'm talking software here - specifically GEDCOM compliant software. Obviously I can add him in on one of my little paper index cards and add in the note there.