As Jerry already mentioned, the posted sample doesn't look correct.
Usually, the format will be mmddyy or yymmdd or yyddd. It would be very
unusual for it to be myyddd. If the final format is the case, what is the
value for October 17th? Two things are at play here. How is a month higher
than 9 handled and is the three digit day field actually a year to date
number or is it the more normal month to date number in which case it
shouldn't be three digits.
To convert mmddyy to a date, use:
CDate(Mid(YourDate,3,2) & "/" & Right(YourDate,2) & "/" & Left(YourDate,2))
This just pulls out various positions in the six digit string and reorders
them concatenated with the date separator.
To convert yyddd to a date, use:
DateAdd("d", Right(YourDate,3) - 1, CDate("1/1/" & Left(YourDate,2))
This adds the number of days in the ddd part of the string to Jan 1st of the
year part of the string. 1 is subtracted from the ddd part because the date
it is being added to is the first of Jan rather than the 31st of Dec. You
could do that but the calculation then has to subtract 1 from 1/1/youryear
to get 12/31/prevyouryear.