Required notice. If a proceeding is commenced under section 6110(h)(4) with respect to any written determination, the Secretary shall send notice of the commencement of the proceeding to any person to whom the written determination pertains. No notice is required to be sent to persons who have filed the petition that commenced the proceeding under section 6110(h)(4) with respect to the written determination. The notice shall be sent, by registered or certified mail, to the last known address of the persons described in this paragraph (b)(2)(v) within 15 days after notice of the petition filed under section 6110(h)(4) is served on the Secretary. For further guidance regarding the definition of last known address, see 301.62122.