The AddressFinder (NCOA) Service scans existing accounts in your database and compares the addresses for those accounts to the US Post Office's database to look for inconsistencies. If the service identifies an inconsistency, it will correct the address in cases when it can identify an updated or standardized address for the Constituent.
The NCOA compares the Last Name field in eTapestry to the Last Name field in the Post Office's database. However, in eTapestry, accounts that have the Family Name Format do not have an identified Last Name, they only have an Account Name. The NCOA Service is not able to parse a Last Name from the Account Name field. For this reason, the service can standardize an address (i.e. it will correct "Street" to "St"), but if the family has moved and registered their new address, it cannot identify the move to update the account.