This submission comprises the raw and processed mass spectrometry data from a high-resolution proteogenomic atlas established in iPSC-derived cortical neurons (a model of human neuron development). The data was collected using quantitative Tandem Mass Tag (TMT) proteomics and integrated with deep long-read RNA sequencing to expand the human proteome's functional landscape. Crucially, the mass spectrometry data provided direct peptide evidence supporting the translation of hundreds of novel protein-coding sequences derived from previously unknown mRNA isoforms. This resource was used to characterize dynamic protein isoform switching (including microexon usage and intron retention) within ASD risk genes during neuronal maturation, offering a critical foundation for reinterpreting pathogenic genetic variation in neurodevelopmental disorders.