This Implementation Guide (IG) also utilizes the profiles detailed in the HL7 FHIR� US Core Implementation Guide STU3 Release 3.1.1 ( https://www.hl7.org/fhir/us/core/ ) based on HL7 FHIR Release 4.

Which was the url of 3.1.1 when it was the latest published but now 4.0.0 is the latest. Other pages do the same "mis-link". It's a bind, as the url we have will always be latest published, there isn't a STU4 permanent link (that I know of) until there is a superseding version. If we say, current, then if current USCore changes in a way that is incompatible with this PDEX, what happens?