@akargeA suggestion to deal with this issue:
A new forum section where readers can post links to stories they read on SOL that the new tags would apply to. The reader would have to list the story, the missing tag, and the location/rough description of at least 1 scene in the story that the tag is applicable to (chapter number, approx location within the chapter).
This would make it a lot easier for mods to retroactively apply tags to stories. Retroactively applied tags would only be added to stories from the forum section after the applicability is verified and ONLY if the author is inactive AND the story doesn't have a missing tags warning from the author due to concerns of spoiling plot.
This way active authors still control their story tags, mods aren't nearly as overwhelmed by the sheer enormity of the task, and the readers are doing the work of identifying the stories with missing tags instead of the mods. I am 1000% sure there are more readers than mods authorized to add/remove story tags...even if you include the authors themselves..lol.
Oh yeah... each "new topic" in the forum section would be about a single story with the story title in the Subject field. Replies would not be open but limited to an acknowledgement and approval/rejection of the recommended tag changes by the mods.
EDIT: I know Laz is the Site Mod and I know authors can mod their own submissions, but I don't know if Laz has authorized anyone else as mods. Thus the way I worded this. Either way, this suggestion shifts the majority of the work to the readers, namely to identify the story, the missing tags, and present information sufficient to quickly locate a verifying scene in the story. Thus the mod just has to read the forum post, check that the author is on the inactive list, open the story to the identified scene, scan it to verify it meets the standard of the suggested missing tag, go to the story description to verify tags aren't purposely excluded to limit plot spoilers, then add the tag if needed and reply to post. One hell of a lot easier to do than trying to retro-tag the entire posted story catalogue and shifts the vast majority of the retro-tagging work to the readers as well as limiting the scope and providing a "checklist" of sorts for both mods and readers for submitted posts.