This is a well-known discrepancy. See
http://www.google.ca/search?q=till+n...iw=904&bih=507 for numerous comments.
It has not been corrected because mostly Christopher Tolkien and Wayne G. Hammond and Christina Scull have only corrected discrepancies where the change is minor. Wayne G. Hammond and Chistina Scull mention in “NOTE ON THE 50ᵀᴴ ANNIVERSARY EDITION” in current publications of
Fellowship:
But those inconsistencies of content, such as Gimli’s famous (and erroneous) statement in Book III, Chapter 7, ‘Till now I have hewn naught but wood since I left Moria’, which would require rewriting rather than than simple correction, remain unchanged.