A few questions:
a. Which version of Word/Excel?
b. Does the Excel column containing the codes have a mixture of code types
(e.g. numeric US codes, alphanumeric Canadian codes, other?). If so, are the
first few codes in the column all numeric? Or is the column formatted as
numeric?

If the column is formatted as numeric or the first few codes are all-numeric
codes, Word may treat the entire column as numeric.If tat is the problem you
may be able to fix it by changing the column format (make a copy of your
spreadsheet first!) so that it is text, or changing the way Word connects to
Excel (I'd try checking Word Tools|Options|General|"confirm conversions at
open", going through the connection process again, and selecting the DDE
option when it is offered). If you change the column format, you will
probably still need to rconnect to the data to get Word to "see" the change.

--
Peter Jamieson - Word MVP