I am more well versed in sexual mature content and the demands for warning tags there, however I do occasionally create and read horror content.
The reason you see some people marking mature at the mere mention of blood is that in clear writing there is a minimum you must follow, but in practice some creators are more strict in their own content (more wary of sensitive audiences or in the case of sexual content, more prudish to be frank). That doesn't mean you have to follow their standards if you don't want to.
Small wounds, slight bleeding or a bloodcovered person (who isnt graphically injured), bloodstains, and possibly also crime scenes where the body has been removed or is not very graphically displayed or detailed should pass without mature content marking if i understand things right.
Heavy violence such as stabbings, heavily graphic injuries where you see innards or flesh ripping open and the like would require mature content marking. I do believe extremely morally heavy deaths such as suicides or child murder may need it too? Just an observation I have made.
If you want to better understand how this plays out on Tapas I suggest looking at the stuff Darkbox puts out (i.e Silent Horror). Darkbox has multiple premium comics and is quite large so eyes are on them and misdeeds would be caught fast. Their Premium comics would be the best go to to understand and study how Tapas staff themselves apply their rules and standards, since Tapas staff immediately overlook their premium content as part of their editorial process.
