Understanding the difference in the ZIP+4 returned for the same address in CODE-1 Plus and Finalist

Products Affected:  CODE-1 Plus, Finalist
The same address is being passed into the coding products but a different ZIP+4 is returned.  Why would this happen?

There are a few instances where this could occur:

1)  If the address was flagged as Delivery Point Validation (DPV) non-confirmed;  If only using the US Postal database and not the Delivery Point Validation database, the US Postal database may return a ZIP+4 while the Delivery Point Validation database suppresses the ZIP+4 as it was a non-confirmed address.

2)  If the address is missing unit or secondary information; if an address is matched but secondary information is not provided, the default high rise zip+4 is applied instead of the ZIP+4 associated with the unit or secondary information.

3)  If the address is missing a firm name; if an address is missing firm information, the default high rise ZIP+4 is applied instead of the ZIP+4 associated with the firm name.
UPDATED:  January 27, 2020