In the Match API, what does address_type to?

The main address types we use are DPA (Delivery Point Address), APR (Approved from LPI i.e. Local Authority Address), PRV (Provisional) or HIS (Historic).  AddressBase incudes data from two sources: DPA addresses come from the Royal Mail, LPI come from Local Authorities.  These are joined together to BLPU which is assigned a UPRN.  Addresscloud favours the DPA address where it exists as this is generally the closest address to a user's expectation as it should match with the address they use to receive mail.  Where an LPI record differs from a DPA address we include this as an alternative version of the address to help improve match rates (you can toggle these on in the API with show_alts=true).  Where no DPA address exists for a UPRN we bring through the LPI record and assign the address type depending on the type of address this is APR, PRV or HIS.