Broad subject that came up in the Star Trek Picard thread. - information not yet in the show itself but had been in trailers (in this characters seen in a preseason trailer but not yet in the show).
Some had not seen the trailers or read articles discussing these characters going to be in show, and considered that information as best not having had been shared. That’s my take FWIW. The other position is that articles discussing those characters being on the show were widely read (our problem that we didn’t read them), and that information shown in trailers is as fair game as what is shown in eps.
Yes, I do think if a thread says “Open Spoilers” all of that - trailers, articles are fair game. Unless it is specified to the contrary. If the OP said that Open Spoilers are just for what is aired on the TV show and other content is to be spoilered then that would be another thing - however, in the case of Star Trek, you’d run into issues of are character backstories from other media (TNG, DS9, etc) allowed under the TV show only rule.