It is finished? It is done?

Sorry to go for the double post on you guys (especially because this is going to be a nerdy one), but something's been at the back of my mind for a couple of chapters and I want your opinion on it.

I noticed that a few chapters ago, John writes "It is done." Now, mentally, we all instantly when to the cross and heard the "It is finished" parallel, but I got to thinking - why did they translate it differently in Revelation than in John's gospel?

So when "It is done" came up again this chapter, I decided to look up the original. Turns out the Greek has two different words too. So at first, I thought maybe I was just reading too much into it - so there's two different words, so what?

But the thing is, it's the same author. And not just any same author - John was an eyewitness to both events. Why would the man who stood AT THE CROSS and listened to the last words of his dying Savior and the man who heard the Word of YHWH from the throne write down anything other than exactly what he heard? Which, in turn, begs my second question: Why would God choose a different word each time? He knows our hearts, he knows specific words carry specific connotations for us - why did He make this distinction?

telew: finished, complete, perfected, paid for
This is the word used in John 19 and in a bunch of different places throughout the NT, like "His power is perfected in weakness" or "He who began a good work in you will bring it to completion."

gignomai: to be, become; to come to pass; to finish, perform
This is the word we find in both Revelation 16 and 21. It's commonly used... but not so much with this meaning. More often that not it has that first "be" or "become" connotation, not really the "finishing/completion" one.

Obviously there are subtle differences in the word meanings, but I think there are also subtle differences in what is being completed. Both events are cataclysmic and decisive. They provide such intense completion, perfection, and fullness, but somehow I feel like they are slightly different sides of the same coin, and I can't quite piece together exactly what it is. Or at least, I can't quite piece together how that slight distinction relates to the slight distinction between the words.

Thoughts?