No. "Ignorance of the law is no excuse" is what you say to the defendant who claims they can't be prosecuted because they didn't know. This is about, in essence, prosecutorial discretion.

If everybody was prosecuted for breaking all the laws they didn't know existed, everybody would be in prison.

Also, the old principle was reasonable when the law consisted of things like "don't kill people or steal stuff" which everybody can be reasonably expected to know whether or not they ever read the book where it's written down. That doesn't quite work when you're talking about every obscure detail of the 70,000 pages in the Federal Register.