ms outlook 2003 sp2

Hi I would like to resolve an issue with the way a date is appearing in my
custom outlook form.

1. I imported about 800 records with a membership start date, and creted a
field that calculates renewal date with this value dateadd ("m", 12, [User
Field 1])

calculations work ok on about half the dates but on the other half it seems
to transpose the order from mm/dd/yyy to dd/mm/yyy.

2. If I Copy these records from the phone list and paste them in an excell
file, and format cells to show dates yyyy/mm/dd half the records dont convert
to that format and remain in mm/dd/yyyy.

I want the custom contact form to display dates as yyyy/mm/dd and cant find
a solution on this forum.

I also would like to know if there is a way to check all the dates in the
database so they all behave the same way.