Normative samples drawn from older populations may unintentionally include individuals with preclinical Alzheimer’s disease (AD) pathology, resulting in reduced means, increased variability, and overestimation of age-effects on cognitive performance. 264 cognitively normal (CDR=0) older adults were classified as biomarker-negative (“Robust Normal,” n=177) or biomarker-positive (“Preclinical Alzheimer’s Disease” (PCAD), n=87) based on amyloid imaging, cerebrospinal fluid biomarkers, and hippocampal volumes. PCAD participants performed worse than Robust Normals on nearly all cognitive measures. Removing PCAD participants from the normative sample yielded higher means and less variability on episodic memory, visuospatial ability, and executive functioning measures. These results were more pronounced in participants aged 75 and older. Notably, removing PCAD participants from the sample significantly reduced age effects across all cognitive domains. Applying norms from the Robust Normal sample to a separate cohort did not improve CDR classification when using standard deviation cutoff scores. Overall, removing individuals with biomarker evidence of preclinical AD improves normative sample quality and substantially reduces age-effects on cognitive performance, but provides no substantive benefit for diagnostic classifications.