US Core v4.0.0 Implantable Device implementation guidance (http://hl7.org/fhir/us/core/STU4/StructureDefinition-us-core-implantable-device.html#mandatory-and-must-support-data-elements) states that:

Implantable medical devices that have UDI information SHALL represent the UDI code in Device.udiCarrier.carrierHRF.

• All of the five UDI-PI elements that are present in the UDI code SHALL be represented in the corresponding US Core Implantable Device Profile element.

This requirement reads like each Device with UDI code must have 5 UDI-PI elements populated.

Zulip discussion indicates that "not all that info is present in every UDI - so an invariant is not practicable"

Please add that clarification to the requirement to avoid such confusion.