Web Forms :: Validation - Restrict Past Dates While Allowing Edits?

I have a form that collects some dates. The users can go to this form any time, view the data, and edit the data.

The user should only be able to enter today or future dates only. We don't want users to go in here and be able to past date these dates.

So I created a compare validator which compares the text box against today's date. This works great. The user saves the form and life goes on.

But then, lets say they come back 1 week later and want to change a date. Now all the old dates will fire this validator and they can't save anything unless they change all the dates to today or newer. This is a problem.

So what I thought was when I load the form with the data from the database, I would just disable the validator if there is a date, and if it's null enable the validator. But this won't work because then they can back-date all of those dates with the validator disabled.

So for the dates that are not null, it shouldn't fire the validator unless they change the date.

When I load the form, I'm going to load all these dates into Viewstate. I'm going to create a custom validator and check the value they enter against the previous date that is in Viewstate. If it matches that date then it is valid, if it doesn't match that date then I will run it through the validator to check for past-date.