Dynamic properties that are requested in $select are listed in the context URL. If a requested property is not defined for an instance of an open type that otherwise matches the request, the instance is part of the response and is represented without the undefined property. Requesting undeclared properties for types that are not open results in an error.

https://www.oasis-open.org/committees/download.php/50850/odata-v4.0-wd04-part1-protocol-2013-09-27.docx https://www.oasis-open.org/committees/download.php/50852/odata-atom-format-v4.0-wd04-2013-09-27.docx https://www.oasis-open.org/committees/download.php/50851/odata-json-format-v4.0-wd04-2013-09-27.docx Applied: https://www.oasis-open.org/committees/download.php/50877/odata-meeting-54_on-20131001-minutes.html#ga_01