Chapter 3 Why identifiers are messy

• Version suffixes: Ensembl IDs can appear as ENSG... .7 and often must be stripped.
• One-to-many mappings: a stable ID may map to multiple symbols (aliases/synonyms).
• Annotation drift: mappings depend on genome build and Ensembl/HGNC releases.

Best practice: keep the stable ID as the key and add symbols as annotation columns.