Math Is Fun Forum

Please help I have a big problem, I hope that you can help me.

I lost an important document in my office, I can remake them totally with Microsoft Word except the authentication code. This is an alphanumeric code written on the document.

Examined my old documents I have uncovered that:
1.    The code is alphanumeric and  it is always made from 4 characters.
2.    The used characters are 16 (0 1 2 3 4 5 6 7 8 9 A B C D E F).
3.    All the documents emitted in the same day have the same code.
4.    In the same day all PC, also of other offices and not connected to the net,       
                emitted the same code.
5.    I enclose you some sequences from old documents:

In date     February  8, 2006    the code is     5628
                February  10, 2006            0433
                February  22, 2006              5667
                February  24, 2006              1234
                March  1, 2006                   941A
                March  3, 2006                     D4C2
                March  8, 2006             72C1
                March  14, 2006              7996
                March  16, 2006              2A84
                March  21, 2006              1DF0
                August 21, 2006             092B
                September  13, 2006             42D1
                September  15, 2006          A20F   

Thanks to all

Carlotta