Flex Plus Award Availability One-Way vs Return
 

I am looking at some ATH-EWR one-way Flex Plus flights in Business. For specific dates, I see O inventory, but nothing on emirates.com
However, if I search for a return EWR-ATH-EWR, with the ATH-EWR segment on the dates I see O inventory, then emirates.com allows me to book it.
Why is there phantom Flex Plus inventory that is only available to book as part of a round-trip?
As a workaround, could I book a return then drop the outbound segment for a partial refund of miles?