Accurate mortality data is foundational for real-world evidence (RWE). Yet relying on any single source, whether administrative (e.g., SSA), broader government registries, or alternative data assets, introduces systematic gaps that distort survival estimates and weaken causal inference.

Single-source datasets suffer from critical limitations:

• Coverage: No single source captures all national deaths.
• Completeness: Missingness across demographic information or death date reduces cohort capture in research
• Timeliness: Lagging data delays near-real-time insights.
• Quality: Inconsistent records undermine outcomes research.

This study investigates the construction of a composite mortality database built by consolidating multiple complementary data sources. The magnitude, consistency, and mechanisms of improvement across four performance dimensions are explored.