Recreating an entire list of dates with a framework that can be quite slow loading, like Ext JS 3.x, sounds counter intuitive. But that's how to resolve this.

I copied my Browser Fixture properties that create the the first Programmatic List. And named these as Secondary Programmatic Dates, etc.

One saves the date whether it is going to be Post(ed) (activated, checked) or Deactivated (unchecked). Then using the secondary list, the date is returned to its pre-test value.

Working with the already existing list seems much faster an approach but IReadOnlyCollection is just that.

Jeff C, Diego, DeLaphante, thanks for the input.