No, but I think it might happen if copyright lapsed in 14 years.
Presumably people would consider a Song of Ice and Fire sequel by GRRM to be "official" and everything else "fanfiction", even if the fanfiction manages to appear in bookstores
But it would only lapse after 28, assuming the author is still interested in pursuing it. 28 years is plenty, IMO.
Presumably people would consider a Song of Ice and Fire sequel by GRRM to be "official" and everything else "fanfiction", even if the fanfiction manages to appear in bookstores