Minor issue: The example has an organizer with classCode='ORGANIZER'. This is not a valid classCode for organizer. In its position in an entry it is an ActClassDocumentEntryOrganizer which has two allowed classCodes: BATTERY and CLUSTER. Probably BATTERY is intended since CLUSTER is usually associated with a specimen.
Using a reference with typeCode of "APND" is not allowed in CDA R2 schema. In that location, a reference is of type x_ActRelationshipExternalReference which allows typeCodes: XCRPT, RPLC, SPRT, ELNK, REFR, SUBJ.