In January 2023, the Medicare 1999-2013 feasibility files were replaced to correct the match status variable (CMS_MEDICARE_MATCH) from 2 (“linkage-eligible but not linked”) to 9 (“not eligible for linkage”) for some records.
These survey participants had given consent for linkage, however they did not have sufficient PII to be able to match under the deterministic algorithm used for this linkage. Therefore they should be counted as ineligible for linkage for purposes of any survey weight adjustments.

For survey years NHIS 2007-2013, the revised feasibility files only contain records for Sample Adult and Sample Child survey participants. All other NHIS participants in these years were ineligible for linkage (CMS_MEDICARE_MATCH=9).