Using deidentified administrative records for non-international undergraduates graduating from 2014–2023 at a large, diverse public research university in the western United States, this study examines how family of origin structures college major choice and how incomplete measurement of family influences may bias estimates linking majors to early occupational status. Leveraging a comparative dyad design, we assess concordance in major selection and divergence in post-baccalaureate occupational standing and post-BA educational attainment across four groups that share progressively more family context: random cohort pairs, non-kin pairs matched on observed sociodemographic characteristics, sibling pairs, and twin pairs. We operationalize occupational standing with a Hauser–Warren–style Socioeconomic Index derived from linked employment records (Steppingblocks/Lightcast), with post-BA education outcomes drawn from National Student Clearinghouse data.