Date Format Matters - FM5.5 to FM8

I'm looking at a file that was converted from FMP 5.5 to FM8. A typical date, as entered, might read "07/12/1962" - that is shown formatted as entered. The same field with date formatted as "Jul-12" style will not display that date, instead it returns the "?" If I remove the leading "0" the date format resolves to "Jul-12". It certainly doesn't seem to violate the M/D or D/M laws. I can also re-enter the date or copy/paste, exactly as is, and the date now formats correctly. There are 12K of them to do - it there a better way? Is this "known" - eg. that a date can be a date yet not be a date. The field takes great exception if I enter 13/12/2005 when the expected format is MM/DD/YYYY. SO the field knows it is a date - it's just the date that doesn't know it is a date - a sort will not sort correctly and the only finds that work are on dates that have been fixed!

Stephen