Happy 10th Birthday Kill la Kill! - and a question about spoilers

Note: This topic contains a spoiler about Kill la Kill

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Ten years ago, on the 4th of October 2013, the first episode of Kill la Kill was broadcast.
An amazing anime with groundbreaking animation, fanservice, and a nice twist around the second half when the protagonist matoi_ryuuko and antagonist kiryuuin_satsuki were revealed to be sisters.

When this series was being broadcast, tagging any post featuring Matoi and Satsuki together with siblings or sisters (and optionally incest) was considered a foul and a breach of the Danbooru guidelines.
All instances of these tags were actively being scrubbed, though in the years that followed afterwards this stance has loosened somewhat.

To take post #2597791 as an example:

• This image was uploaded in 2017, 4 years after broadcast.
• I left a comment mentioning this issue and removed the tags.
• The tags were then added and removed again until they were added for the final time in 2020.
• My comment has since accrued a number of downvotes, so there clearly is some sentiment against this way of thinking.

Looking at some numbers ten years later, it still hasn't completely settled.

In the about:spoilers guidelines that were applicable during that time, spoilers were considered as distasteful as public sex to your pastor
These have since been replaced with the more general help:community rules where spoilers are only mentioned within the context of comments and to use spoiler tags.
The howto:tag page only mentions spoilers when the image itself is a spoiler (ie. the death of a character)

Because this will undoubtedly happen again in the future:

What is the tagging policy when the tags themselves can be considered spoilers?

Should we strive for a complete archive and just add tags the moment this information becomes public?
Should they never be added forever and ever all the way in perpetuity?
Should they be added after its broadcast has been completed?
Added after X amount of time?

Making it short:
I think adding the accurate tags after a (short) amount of time after the series has finished should be fine.
For Kill la Kill, all images with both characters appearing should be tagged as siblings. Not adding it would also mean, that you won't be able to search or blacklist all incest images of them.

At the very least after the initial broadcast was my gut feeling as well.
Hope that others will share their thoughts too, so we can establish how much time X should be so that this can be formulated in a guideline and then added to the howto:tag page accordingly.

Nothing too specific like up to the second precise, but roughly knowing whether we are talking about weeks / months, or even "the day after the final episode" would be useful.

Regardless, I'lll first do a pass through the kill_la_kill tag to update the related tags.