When Rev 16:14 says
For they are the spirits of devils, working miracles, [which] go forth unto the kings of the earth and of the whole world, to gather them to the battle of that great day of God Almighty.
and then verse 16 continues the thought from verse 14 - And he gathered them together into a place called in the Hebrew tongue Armageddon.
I think it is abundantly clear that verse 15 is a parenthesis, yet if you do not want to see there is nothing I can write hear that will cause you to see it.
In that sense I guess you could say that it is a parenthetical verse, but that doesn't mean it doesn't fit the context of the other verses and doesn't mean you can try to say that He already came before that. How could you make any sense of putting that verse there if He will have already come before that? If He already will have come before that then that would mean the verse was just put in there for no reason at all.