Inspector Sands
Back in the 90s, subtitle files were delivered on a 3.5" floppy disc, one disc per programme, which would be loaded along with the transmission tape and the subtitles were inserted according to the timecode being read off the tape. Using the discs live to air was replaced with a file-based delivery system in around 1996/7ish, although the discs were still delivered to pres as a backup.

When I was in pres it was all file transfer, but remember it being a convoluted system of FTPing it from a server to a local shared drive and then from there inserter.

There was an unfathomable panel which we as operators were supposed to be able to nudge subtitles back into synch if there'd been a last-minute edit of the programme or if the TC that the subtitler had worked from differed from the TC actually on the TX tape (this happened more than it should have done!). The nudge panel allowed you to add or subtract hours, minutes, seconds and frames as an offset between TC and Subtitles file. A few seconds out was ok, but you needed a degree in pure mathematics to work out the offset between some files. On occasions you'd be nudging subtitles live to air, literally watching off-air to see if your nudge had made things better or worse!! Sometimes it was easier to abandon subs and put out an apology subtitle.

Yes, that was TSTS (Teletext Subtitle Transmission System I think) in the NTA. It did have a nice function where it allowed you to nudge the subtitles to a programme offline on your local monitor and then when correct put them to air. Once playout moved to the DTA it was replaced with basic inserters above each VT machine where you had to do it live.

However it was rare to notice it on air; the routine when lining up tapes was to check the subtitles matched at the beginning and the end of the programme, then you could be 99% sure they were correct - they'd rarely go out of sync in the middle and then correct themselves for the end. It wasn't encouraged to nudge them live on air, but it did happen and it had the potential for a right mess.

The maths was fairly simple though, but needed time to work out. The trick was to listen out for a distinct sentence and make a note of the timecode... then find watch till you saw the subtitle for that sentence and subtract the two timecodes. If you were really stuck you could open the subtitle file in notepad and find it that way.