This is improver iCalendar sytax. No "UID", no "SEQUENCE", etc. Maybe you weren't trying to be precise?
You can only add events to an existing request with an "ADD" method; not a "REQUEST".
Dan's point was not just the scenario for adding an occurrence, but changing some other details in an occurrence so that a single REQUEST would actually obliterate the differences. You are right, for this you might be able to use a second REQUEST with an incremented "SEQUENCE" value and a "RECURRENCE-ID" to show the different property values from the original occurrence set. That is, as long as the occurrence was defined in the occurrence set defined by the initial "REQUEST".
-- Frank