Years ago prompter text was indeed used for closed captioning, but those computer scripting “notes” you refer to were formatted to be invisible to what was being sent to captioning. This was back in the early days of NRCS systems, such as Basys.I do TV, and you can't use teleprompter text in closed captioning. For one thing, there are notes in the prompter for which anchor should read, breaks in stories, etc., that wouldn't work in closed captioning.
Later stations would use an offsite (in another state) captioning service that would dial into the station’s audio and caption what they heard. Of course those captioners could not see the video output.