Facts
[D.], born in 1935, received a half-disability pension as of April 1, 1987, and a full pension as of April 1, 1999, with a supplementary pension for his spouse [A.], born on September 25, 1937. When A.'s ordinary old-age pension (AVS) was determined as of October 1, 1999, the Compensation Fund for Milk and Agricultural Organizations (Compensation Fund Milk) recalculated the disability pension. It then split (splitting) the income of the spouses [D.] earned from 1970 (the year the spouse entered Switzerland) to 1986 (the year preceding the disability insurance case) and took into account ten credits for childcare. The other calculation factors remained unchanged. By decision of October 5, 1999, the IV Office of the Canton of Zurich set the (capped) disability pension at CHF 938.- per month as of October 1, 1999 and discontinued the supplementary pension for the spouse. On the same day, the Compensation Fund Milk granted [A.] an old-age pension of CHF 1'118.- per month.Considerations
According to Art. 36 para. 2 InvIA, the provisions of the OASIA apply by analogy to the calculation of ordinary pensions of the disability insurance. Arts. 29bis to 33ter OASIA contain the "Bases for the calculation of ordinary pensions" of the AVS. Art. 29quinquies para. 3 let. a OASIA provides for the splitting of the spouses' income when both spouses are entitled to a pension. However, according to Art. 29quinquies para. 4 let. a OASIA, only the income between January 1 following the completion of the 20th year and December 31 preceding the occurrence of the insurance case of the spouse who becomes the first beneficiary of a pension is taken into account.
Art. 31 OASIA provides that upon the new determination of an old-age pension, the calculation provisions in force at the time of the first calculation of the pension remain decisive. Art. 33bis OASIA regulates various issues related to the "replacement of a disability pension" by…