I took ~5 minutes to look at it in the past month or two, but they changed a lot about how the SDK is distributed, and I haven’t taken any time into looking into URLs that were saved in the wayback machine, and/or solving this in a more robust manner.
Though, I hadn’t thought about this one weird trick to list URLs in the wayback machine:
One might use that to gather an SDK from around the same time to verify things work, and then start updating slowly if needed.
With that said, it’s not strictly required to update Nixpkgs, since you can conveniently think of it as an input to the toolchain, and in the end the result doesn’t really depend on anything from Nixpkgs, the way those applications work.