It's imply the historical fact of JRRT's writing.
Most of us would have been happier if JRRT had not been
the master of the "Unfinished
Tales". Or perhaps not, when I think of some of his "later writings".
Write your own "History of
Galadriel and
Celeborn" if you like (as mentioned in other threads, some people have constructed private versions of
Middle-earth's history, picking and choosing). There's certainly a ton of fan-fiction around - which, as One commentator suggested, includes Christopher
Tolkien's 1977 Silmarillion; with a major difference: it had in principle authorized by JRRT.