if I go back to the Form at a later date, that new Part Number wouldnt be in the Combo Box
It can be, if you do it right.
If you make the Combo Box source be the actual field from the table you are populating, it will work. It will allow you to add new entries, and the next time you go in there, your new entries will be available to select from too.
The SQL code for the Row Source of that Combo Box will look something like:
Code:
SELECT DISTINCT TableName.PartNumber
FROM TableName
ORDER BY TableName.PartNumber;