Generative artificial intelligence (AI) is increasingly making its way into fashion practice through the possibilities it offers for rapid visual ideation, variation, and experimentation. These capabilities extend the scope and pace of creative exploration, but their use in the development of functional apparel poses significant questions about design direction, technical accuracy, authorship, and creative authenticity. The present study investigates an integrated digital workflow that combines human creative judgment, AI-assisted visual ideation, Adobe Illustrator-based 2D vector development, and CLO 3D virtual prototyping to maintain individual design direction in structured outerwear. The study applied a qualitative, practice-oriented design research approach using an avant-garde blazer as the focal design case. The workflow involved human-led concept development, AI-assisted controlled variation, technical reconstruction in Adobe Illustrator, and 3D virtual prototyping and refinement in CLO 3D. The Collaborative Authenticity Framework (CAF) was developed through this process in three interconnected phases: Conceptual Anchoring, Algorithmic Expansion, and Digital Prototyping and Curation. Three design variables were examined through modifications to five garment components: lapels, collars, sleeves, closures, and garment proportions. The findings indicate that AI can broaden the design exploration space, but AI-generated visual outputs require human interpretation, selection, technical reconstruction, and refinement before they can function coherently within a structured garment-development workflow. The study therefore conceptualizes creative authenticity not as the absence of computational assistance, but as an active process through which the designer maintains meaningful control over conceptual direction, evaluation, technical transformation, and final curation.