26 CFR §25.2504-2

1. (a)Gifts made before August 6, 1997. If the time has expired within which a tax may be assessed under chapter 12 of the Internal Revenue Code (or under corresponding provisions of prior laws) on the transfer of property by gift made during a preceding calendar period, as defined in § 25.2502-1(c)(2), the gift was made prior to August 6, 1997, and a tax has been assessed or paid for such prior calendar period, the value of the gift, for purposes of arriving at the correct amount of the taxable gifts for the preceding calendar periods (as defined under § 25.2504-1(a)), is the value used in computing the tax for the last preceding calendar period for which a tax was assessed or paid under chapter 12 of the Internal Revenue Code or the corresponding provisions of prior laws. However, this rule does not apply where no tax was paid or assessed for the prior calendar period. Furthermore, this rule does not apply to adjustments involving issues other than valuation. See § 25.2504-1(d).
2. (b)Gifts made or section 2701(d) taxable events occurring after August 5, 1997. If the time has expired under section 6501 within which a gift tax may be assessed under chapter 12 of the Internal Revenue Code (or under corresponding provisions of prior laws) on the transfer of property by gift made during a preceding calendar period, as defined in § 25.2502-1(c)(2), or with respect to an increase in taxable gifts required under section 2701(d) and § 25.2701-4, and the gift was made, or the section 2701(d) taxable event occurred, after August 5, 1997, the amount of the taxable gift or the amount of the increase in taxable gifts, for purposes of determining the correct amount of taxable gifts for the preceding calendar periods (as defined in § 25.2504-1(a)), is the amount that is finally determined for gift tax purposes (within the meaning of § 20.2001-1(c) of this chapter) and such amount may not be thereafter adjusted. The rule of this paragraph (b) applies to adjustments involving all issues relating to the gift including valuation issues and legal issues involving the interpretation of the gift tax law. For purposes of determining if the time has expired within which a gift tax may be assessed, see § 301.6501(c)-1(e) and (f) of this chapter.
3. (c)Examples. The following examples illustrate the rules of paragraphs (a) and (b) of this section:
4. (d)Effective dates. Paragraph (a) of this section applies to transfers of property by gift made prior to August 6, 1997. Paragraphs (b) and (c) of this section apply to transfers of property by gift made after August 5, 1997, if the gift tax return for the calendar period in which the transfer is reported is filed after December 3, 1999.