The longer answer is: it depends on the timing of the retrieval. Let’s say that you register a metadata record with us with no affiliations and then come behind that initial registration later and add affiliation metadata to an existing DOI. If you then attempt to retrieve that metadata record in our REST API, there will be a lag before you see the affiliation metadata appear in the REST API. It can take us up to 24 hours to index (or, reindex in this example) a submission.
Also, is it possible to find under which crossref schema version a doi was submitted with?
Unfortunately, neither the JSON output in the REST API nor the XML output in the XML API includes the XML input schema that was used for the registration.