Both these copies of 1b feature the original artwork of the 1960s.  At first sight they seem identical. The reason they are included in this gallery is because many collectors believe that the indicator of a revised version of these book is something to do with the 'key' logo towards the bottom of the cover.  Certainly the key logo was situatued on the right of the earlier books and at a later date was placed in a black box and moved to the left.  But this change did not coincide with the revision of the artwork, as the books above demonstrate, but took place a little earlier.  So although all the '1st revision' books will have the later style key logo, so will some of the original version books.