More to the point at hand, can you use the term
"Encyclopædia
Britannica", which is a registered trademark even though a creative
work with that name has its copyright expire? This question is of
particular personal importance because my name is now attached to
the project on Wikisource, even though people other than I have
made the edits to put that name on the project. If we need to
rename the project, it needs to be done sooner than later.
Yes you can use it :)