User blog comment:The ASL Pirates/The Supernovas Where Are They Now?/@comment-24769684-20150515090653/@comment-26082375-20150515200555

The difference between Z and Shiki is that Shiki appeared (as a name) in the manga before he was turned into the antagonist of the Strong World movie. Oda had invented him already, and therefore while the character of Shiki is canon, the events of Strong World are not. Z was created for the sole purpose of Film Z, and so even though Oda did design him and write his story, nothing about Film Z is canon.

About the gender neutrality issue, oftentimes they do refer to other characters in a gender neutral way, saying things that more literally mean "that person" instead of "he" or "she." In this particular instance in chapter 700, however, they did specifically use "the man."