If you want Excel to interpret the number as a date, you have to type it in
one of the formats that Excel recognizes. 6 digits with no punctuation is not
one of those formats. 100804 may mean October 8, 2004 to you and me, but Excl
has no way to know that you don't mean simply the number 100,804.
Once you have entered the data so that Excel recogizes it as a date, you can
simply change the cell's format to yyyy-mm-dd or whatever you wish.
BTW, changing the format of the cells to a date format BEFORE you enter the
data doesn't relieve you of the obligation to either (1) type the date with
date separators, or (2) run a macro to convert the number you type into a
date.
