Citing confusion among providers, the Centers for Medicare & Medicaid Services has issued a chart of critical dates between now and May 23 for Medicare fee-for-service (FFS) implementation of the National Provider Identifier (NPI). The chart illustrates expected claim results for different identifiers, or combinations thereof, submitted in the primary provider fields on the Medicare FFS 837P and the CMS-1500. When the chart indicates that claims will be paid, this would be only if no other errors (non-NPI) exist, CMS notes.