We have a "policy" of only hosting the 2 most recent major releases. We're currently still in the process of transitioning to the latest v16.x release, hence why the v14.x images still exist on the official mirrors. At some point after we complete the v16.x release, then the v14.x images will be purged.

I recall at one point there was an old out of sync mirror that had some old images on it, but I don't think they went back as far as v12.x.

TBH, I'm not really sure how you'll be able to work around that, but if you share a bit more about what you're trying to achieve, then perhaps I might have some ideas?