• A pseudonym is not a nickname (nickname usually only replaces a given name) Some references:
  • https://www.britannica.com/topic/nickname
  • https://www.copyright.gov/circs/circ32.pdf
• Pseudonym - may or may not be for the purposes of anonymity
• Legal should be equivalent to official. It should not map to usual - it could be a narrower map to Usual I suppose  - a usual name may or may not be legal and a legal name may or may not be Usual

Lastly the the FHIR name-use code system is deficient and should be updated (Beyond the scope of this initiative)

Relates to: https://jira.hl7.org/browse/FHIR-40904