Why not build the regional breakdown purely from ancient DNA?

Ancient genomes are sparse, uneven, and sometimes highly degraded. Coverage, sampling bias, and damage make it impossible (for now) to deliver province-level precision from ancient DNA alone. Instead, the report uses living reference panels that show stable, fine-scale structure across Iberia, interprets those panels through Iberia-specific ancient DNA and historical literature, and validates patterns against curated ancient genomes.