R4 New Cardinality Requirements and Conversion from STU3 - ExplanationOfBenefit

With R4, we are noticing that the cardinality changed from 0…1 or 0…* to 1…1 or 1…* for several elements of an ExplanationOfBenefit resource from STU3:

-Created
-Insurer
-Provider
-Outcome
-Insurance

We would like to think these would always be found in an STU3 resource of the same but since they are not required, how would we handle with a conversion to R4, when not present?

Elements, such as created etc., can have extensions. See http://hl7.org/fhir/R4/extensibility.html
In your R4 instances elements like ExplanationOfBenefit.created do not get a value, but do an extension. The explanation could explain that no ordinary value is available. Maybe use http://hl7.org/fhir/R4/extension-data-absent-reason.html with a value of “unknown”