Currently, our newly introduced ServiceRequest profile defines the occurrenceData data element to be MustSupport; indicating that every compliant FHIR server must be capable of populating this field. 

Pretty much all community resource referrals are ongoing and do not have a specific occurrences. For example, imagine a foodbank referral resulting in fortnightly trips to a community foodbank. What single "occurrence" date could be meaninfully populated into this data element. 

While some services happen once, but the care coordinator would not request specifically when it is to be done. That would be decided by the availability of the requestee.

Occurrence should not be MustSupport. MustSupport should be removed from this element. 

If there's some reason that implementers have identified that requires support for this field, this rationale should be:

1) documented in the specification.

2) the allowable data types for occurrence should be updated to permit Period, such that, in scenarios like the above described food bank, implementers could populate occurrencePeriod.start with the date of the referral being accepted.