Is AddressFirst a separate API to the Match API?

The Match API is the system through which we match the addresses, it is independent of the data being provided.  AddressFirst is our hybrid product which combines data from the Royal Mail (including the Not Yet Built and Multi Residence files) with data from the Ordnance Survey (AddressBase Core).  The advantage is that it takes a PAF centric view of addressing and therefore matches PAF exactly.  Some addresses such as New Builds can take some time to arrive in AddressBase and some small businesses in shared premises are excluded.  AddressFirst fixes this assigning rooftop level coordinates to these addresses where possible falling back to postcode coordinates where these are not (e.g. for a new housing estate).  The disadvantage is that we will not always be able to return a UPRN as the OS own this process.  The vast majority of addresses will have a URPN though.  You can learn more here: https://blog.addresscloud.com/addressfirst/.