data in drop down list is limiting number of entries
 

I have a worksheet with several drop downs created using 2003 I want to add
to one of the columns which contains numbers stored as text (looks like,
-0451) I can add to the column and the validation box has the range of cells
listed, but when I test the drop down the additional numbers are not there.
It seems to be limiting the amount of entries (15 entries only) in this
column only. In the other columns I can add as many entries as I want but all
of those entries are text only. Can anyone please help?