Section 
6659, added 
Pub. L. 97–34, title VII, § 722(a)(1), Aug. 13, 1981, 
95 Stat. 341; amended 
Pub. L. 97–448, title I, § 107(a)(1), (2), Jan. 12, 1983, 
96 Stat. 2391; 
Pub. L. 98–369, div. A, title I, § 155(c)(1), title VII, § 721(x)(4), July 18, 1984, 
98 Stat. 693, 971, related to additions to tax in case of valuation overstatements for purposes of the income tax.
Section 
6659A, added 
Pub. L. 99–514, title XI, § 1138(a), Oct. 22, 1986, 
100 Stat. 2486, related to additions to tax in case of overstatements of pension liabilities.
Section 
6660, added 
Pub. L. 98–369, div. A, title I, § 155(c)(2)(A), July 18, 1984, 
98 Stat. 694; amended 
Pub. L. 99–514, title XVIII, §§ 1811(d), 
1899A
(57), Oct. 22, 1986, 
100 Stat. 2833, 2961, related to additions to tax in case of valuation understatements for purposes of estate or gift taxes.
Section 
6661, added 
Pub. L. 97–248, title III, § 323(a), Sept. 3, 1982, 
96 Stat. 613; amended 
Pub. L. 97–354, § 5(a)(42), Oct. 19, 1982, 
96 Stat. 1697; 
Pub. L. 98–369, div. A, title VII, § 714(h)(3), July 18, 1984, 
98 Stat. 962; 
Pub. L. 99–509, title VIII, § 8002(a), (c), Oct. 21, 1986, 
100 Stat. 1951; 
Pub. L. 99–514, title XV, § 1504(a), Oct. 22, 1986, 
100 Stat. 2743, related to substantial understatements of liability.