Excel force date to NOT change

The spreadsheet I am working on involves well over 100 cells, each with (possibly unique) dates, however for simplicity we will say that I have just 2 cells to work with, A1 and B1. In A1 I want to enter data (could be text, or a number) ONE time...let's say on Monday. I want to use something like an "IF" statement in B1: (If A1 > "" then B1 = date (of data entry) I want this date to be static (non-changing); in other words, I don't want that date to update on next Friday when I open the file to work in it again. "Now" always updates. "Today" always updates. I do not want the date to keep changing to the current date, and I don't want to enter a date in the associated cell every time I enter data. I'm really not sure this is possible using the standard Excel functions, but maybe someone else has an idea...? I've considered using VBA, but I'm not sure that's the best way to go either. TIA!