Maybe not.
Works that were created but not "published" before 1978 will not enter the public domain before the end of 2002. This gets complicated, and it's not too common. If you have such a case, ask about it.
A borderline example is the classic "Seven Pillars of Wisdom" by T. E. Lawrence, which was actually printed and privately distributed, but not "published", in 1922. We haven't been able to confirm any pre-1923 "publication" for this.