It depends on the intent of the person writing the script and what the production staff want for a story. I know younger people think that before the internet there was no way to find information on a subject, but no that wasn't the case. You couldn't get something in 30 seconds yes but there were methods of finding information and verifying things. Plus often the sources were more reliable and at least researched to a degree and not just posted on someone's website as fact without anyone checking on the validity.I'd put it on a sliding scale. The OS continuity effort is still impressive because all there was to refer to were scripts, production documents and people's memories. When TNG came along a number of Star Trek reference books were quite easy to find, and of course in the internet age, forget about it.
TV production is always running at high speed. Getting 22 episodes of season done doesn't give a lot of time for double checking. It can be done but again the emphasis is on a good entertaining story that can be filmed within budget over a few days.
Both TOS and TNG had times where scripts were being written and rewritten while an episode was being filmed; and there were times that scripts weren't even fully finished when shooting began.