It's not clear from the article, but my reading is that while the bug was introduced 12 years ago, it was discovered and fixed only now.
Which is different from knowing about it but ignoring it for 12 years.
Which is different from knowing about it but ignoring it for 12 years.
It could have been discovered quite some time before that, and going by some tweets already posted (caveat: I've not verified anything here) some parts of it at least we're noticed, and Dell notified about them, in 2019.