This paper investigates the impact on labor supply of changes in the Social Security earnings test in 1996 and 2000. We highlight how the persistence of labor supply choices influences both responses to policy changes and the estimation of such responses. We do this in two ways. First, we use data from the Health and Retirement Study and the Current Population Survey that allows us to compare employment transitions across cohorts that are differentially affected by changes in the earnings test rules. We show that conditioning on last year’s employment status is important in identifying responses to current earnings test changes. Second, we test the effect of not only current but also anticipated as well as past earnings test parameters which cohorts faced at earlier ages. We find that past and anticipated future rules influence current employment and earnings. Our results help to identify an effect of earnings test changes affecting ages 65-69 on employment at younger and older ages, which suggests caution about the use of neighboring age groups as control groups in analyzing responses to the earnings test. We also show that earnings test changes that were initiated in 1996 had an important effect, in addition to the changes in 2000 that have been extensively studied.