26 CFR 301.6229(e)-1: (e)-1 Information with respect to unidentified partner.

(a) In general. A partner who is not properly identified on the partnership return (including an indirect partner) remains an unidentified partner for purposes of section 6229(e) until identifying information is furnished as provided in § 301.6223(c)-1.

(b) Effective date. This section is applicable to partnership taxable years beginning on or after October 4, 2001. For years beginning prior to October 4, 2001, see § 301.6229(e)-1T contained in 26 CFR part 1, revised April 1, 2001.