This code system https://fhir.hl7.org.uk/CodeSystem/UKCore-NHSNumberVerificationStatusWales defines the following codes:

CodeDisplay
nnNumber present and traced using Welsh NHS AR
01Number present & traced
02Number present but not traced
03Trace required
04Trace attempted – no match or multiple match found
05Trace needs to be resolved (NHS number or patient detail conflict)
06Trace in progress
07Number not present and trace not required
08Trace postponed (baby under six weeks old)