Some dates recognized as dates, some dates not recognized. Why?

Question

Here is a list of dates:

04-22-11
12-19-11
11-04-11
12-08-11
09-27-11
09-27-11
04-01-11

When you copy this list in Excel, some of th

Answer 1

I come across this problem when I tried to convert to Australian date format in excel. I split the cell with delimiter and used the following code from split cells then altered the issue areas.

=date(dd,mm,yy)