I'm sure that tagging all of these stories would take a while, and perhaps some sort of guidelines should be set about old stories that were written before current policies on content. But that doesn't mean we can't start to expect that people start to tag their current or future work.
Insofar about violent content, well, just throw in an "nc" or "viol" tag, depending on what exactly is going on in the story. For stories that contain sadomasochism, well, "bdsm" or "sado/maso" are reliable enough tags in my experience.
Tagging a story simply means that you're letting the readers know what is going on in the story, it doesn't constrict or limit your creativity. You can start off your grand tale of sordid smut with Jack McHung getting it on with Katie O'Stacked and tag it as simply "m/f." But say after a few entries, Jack's having Steve Goesdeep join in with and without Katie so now you just update it to "m/f m/m mmf." But, say, Jack loses a bet with a genie and now becomes Jane Futasweetie on occasion, so you can toss in a "futa" or "tg" tag for completeness's sake.
I don't know, this is just my experience in writing stuff outside of LPSG, though. Everywhere I've submitted fic to outside of LPSG, this sort of tagging is pretty much expected and unextraordinary.