This is an odd one.

It was originally published in 1983 as part of the omnibus collection, The Omega Point Trilogy, along with the previously published Ashes and Stars and The Omega Point, but was later published separately by Gateway/Orion in 2012.

Thus, one could argue that you really shouldn't attach an item to this record if you don't have the 2012 Gateway/Orion edition, ISBN 978-0-575-12991-7.

However, given that whether it is officially sanctioned or not, it is Acknowledged Practice within the LibraryThing Fen sub-culture (and others as well) to create distinct entries for stories of various length that appear within a serial publication or anthology/collection, treating them as distinct items in their own right, that would be contrary to common practice.

Just remember, don't combine this record with the record for The Omega Trilogy, even if your copy of this work is, indeed, physically bound within that Omnibus volume. And, if it is physically bound within that volume, don't use it's ISBN, as that will attempt to force a merging of records.