re: "Im attaching examples of the original and the copy ( not copy and paste) but using the edit option"
What do you mean by "using the edit option"?
I guess you aren't getting my point, so I'll try one more time.
Including examples of the before and after doesn't help unless we know how the dates got in the original cell in the first place.
Click on the cell that contains 29-Dec-10 in the original document and tell me what it says in the formula bar. Does it show 29-Dec-10 or does it show a formula?
If it shows 29-Dec-10 then I see no reason for it to change when copied to the new document - although I don't know what you mean by "using the edit option" yet.
If it shows a formula, such as =TODAY(), then the formula is going to be evaluated and you'll get the current date.
We're still missing key pieces of information in order to help you.
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