“Q What if the taxpayer does not receive the Collection Due Process Notice because the IRS did not send that notice by certified or registered mail to the taxpayer's last known address, or failed to leave it at the dwelling or usual place of business of the taxpayer, and the taxpayer fails to request a Collection Due Process hearing with Appeals within the 30-day period commencing the day after the end of the five business day notification period?”

and surprise, surprise; does the IRS think they violate the law when they completely fail to deliver the notice…of course not! The answer to this question says:

“A Notice of Federal Tax Lien becomes effective upon filing. The validity and priority of a Notice of Federal Tax Lien is not conditioned on notification to the taxpayer pursuant to section 6320.”