How to discover if the 2-digit DPBC unique to each address in CODE-1 Plus and Finalist

The 2-digit DPBC is typically the last two digits of the house number and will not be unique for each address in the US Postal database.  A completely different algorithm for determining the DPBC is used for high rise records (addresses with apts, suites, etc.). 
UPDATED:  April 17, 2017