Hey Glenn ,
To link the address number and the concerned BP, use BUT021_FS and ADRC tables.
Ensure you have the correct address maintained there .
Also assuming you have settings in pposa_bp for org unit and user maintained .
Note 676496 - Incorrect delivery address in third-party order processing
As per the standard system behaviour, a ship to address is either defaulted from the address of the company or the address maintained in PPOMA_BBP (attribute ADDR_SHIPT). If you use the ADDR_SHIPT attribute in PPOMA_BBP, then in the Portal (SRM Administration - Maintain Internal Business Partner) is used to setup the user's address within his/her company.
If you mark this address as "Ship to Address", when you save the address, an address number will be provided. Assigning this number to attribute ADDR_SHIPT in PPOMA_BBP and setting the address as default, it should appear as the "Ship to Address" when the user creates a shopping cart.