They didn't have any trouble during the drug war when new variations were made because they weren't illegal -- the government made all variants illegal and continued on. That's what they do when they care. When they don't care they pretend there's nothing they can do.

https://en.wikipedia.org/wiki/Federal_Analogue_Act

> ...any chemical "substantially similar" to a controlled substance listed in Schedule I or II to be treated as if it were listed in Schedule I