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It sounds like there is a mix of dates
Excel is interpreting those dates it can as standard UK dates the others
it is leaving as text.

I belive Andy's suggestion of using the Text to Columns will work if you
follow the following steps.

Backup the file before you start
Select the original column of dates
Data\Text to Columns
Step1: delimited
Step2: no delimiters selected
Step3: Column Data Format as Date type MDY
Finish

This should convert all of the dates into Excel dates in the form you
need.

Please give it a go and let us know how you get on

hth RES