[gutvol-d] newbie question: copyright editions of public domain works

I inherited from my grandfather 25 years ago 4 collections from his library. He was a Baptist minister (read poor). The first collection is the 11th edition of the Encyclopedia Brittanica published 1910-1911. The other three collections are editions of works that were public domain at the time of the edition (eg `Best Known Works: Defoe'). The copyright dates range from the mid teens to the early forties. But what are these copyrights copyrighting? I can understand editor comments, translations, pictures, etc. But what if spelling/grammar was modernized? Or, portions cut or moved? Would these books (~120 volumes) be of any use? Apologies for my ignorance, Greg Smith