Display Current Date With Specific Formatting In Cell Only Once

I have a blank template workbook containing several sheets which gets copied, filled out, and saved many times. One of the sheets in this workbook has a 'Date' cell on it which needs to display the date on which the rest of that sheet gets filled out, but it shouldn't change if the sheet receives changes later on. The format of the date cell should read, for example; Feb 28, 2012.

I've been trying to figure out how to do this, and I think I've got something - one of the other cells on this particular sheet will receive a data entry once, at the 'creation' of a fresh copy of this template. This cell - Cell L3:Q3 - will not be changed at any further time, as most of the other cells may be subject to. My thought is this: Upon the data entry into the L3:Q3 cell, the date cell - AA1:AC1 - would get the current date inserted into it, and wouldn't change again, unless somebody wanted to manually do so.

How could I do this?