Catalog endpoints read across all sellable objects (product variants and bundles) without requiring you to know which type a value refers to. This matters for SKU-driven workflows like barcode scanning, point-of-sale lookup, and syncing from an external inventory system, where a SKU might belong to either object type.
Lookup by SKU returns the matched object along with a catalog_object_type discriminator, so you can branch on whether you found a variant or a bundle. SKUs are unique across the catalog, making this a reliable exact-match entry point into catalog data.