Help Adding date to cell if another cell status changes

[zach.shupp]

I have an excel file that we add data too for assignments and I want the date to auto popuate if the status is changed to Mitigated, Escalated, or offline. I wrote the below function which works but when i open it the next date the current date is written to those cells. I need help creating a function that writes the date when the status is change and then leave the date alone unless the status is changed again.

I have attached an example of what i have and below is the function, I'm not the greatest with excel and that's why i am asking for help.

Functions:

=IF(G14="Mitigated",TODAY(),IF(G14="Escalated",TODAY(),IF(G14="Offline",TODAY(),"")))