Background/Objectives: This study evaluated whether linear cephalometric measurements show systematic differences in their central values across birth cohort groups in adults from a clinical population and analyzed the implications of these differences for clinical interpretation when norms and clinical deviations are used as reference frameworks. Methods: A cross-sectional observational analytical study was conducted on the basis of 604 lateral cephalometric radiographs of adult patients. Eleven linear cephalometric measurements were obtained and compared across predefined birth cohort groups (<1980, 1980–1989, and 1990–1999) via robust estimators of central tendency through median regression models adjusted for sex, age group, and sagittal skeletal classification. Results: Several linear cephalometric measurements revealed different central values between birth cohort groups, even after adjusting for relevant covariates. Cranial length, anterior cranial base length, posterior facial height, and posterior cranial base length presented lower adjusted median values in the 1990–1999 cohort than in the <1980 cohort. The effective maxillary length and maxillary length also differed between these cohorts. Mandibular measurements, including mandibular length, corpus length, and ramus height, presented the largest adjusted median contrasts between cohorts. These cohort-associated differences were not uniform across all measurements. Conclusions: Routinely used linear cephalometric measurements present different central values across adult birth cohort groups under comparable clinical conditions. A cephalometric value's relative position within its reference distribution may vary by birth cohort. This suggests that using fixed reference means and standard deviations could lead to systematic misestimation in adults from different birth cohorts. Cohort-aware interpretation is valuable in routine cephalometric assessment.