I think the word-final sigma has been found in manuscripts dating to the 1st century BCE, but I think its use was only in cursive and not universal. So, I think

I think the word-final sigma has been found in manuscripts dating to the 1st century BCE, but I think its use was only in cursive and not universal. So, I think you're basically right; certainly majuscule scripta continua documents like the Codex Sinaiticus or Vaticanus wouldn't have used it.