determine if cell is empty and return date

I have a workbook with multiple worksheets. Sheet 1 contains columns with dates (a schedule of activities) which are changed frequently by a column which adds days to the dates and each column with dates has a column to mark an item complete. When an item in the schedule is marked complete it returns a date of completion. So to recap.

Column A - list activities in a schedule
Column B - a list of dates which change
Column C - a number that indicates how many days to change the day by (1 to add a day or -1 to take a day away etc.)
Column D - a column to mark items on the list complete
Column E - a column with dates that appear when items on the list are marked complete.

On Sheet 2 I want to track the original date (because the dates will change) and the final date. Tracking the final date should be easy it's the original date causing me a dilema. How can I write a macro that will record the original date from sheet 1 onto sheet 2 but not update to the new date(s) if they are changed? I can't think of a formula that I can use for this so I'm guessing that it will have to be a macro.

I have attached and example

Thank-you in advance.