Well, this is where you are using EXCEL to STORE data, and it stores CALCULATIONS. The calculation of date is always moving.
You need to insert another column, that controls the entered date, and the current date (existing formula). The first colum checks for an entry on the second one, if it is entered, then don't change the date. If it is BLANK, then allow the dte to go to the currect one!
Have fun with that.
You can always place an entry into a DATABASE, and the date will never change, unless you want it to. If you don't have any EXCEL formula experience, or ACCESS experience, then learn ACCESS!