Ask which authority issued the identifier and for what purpose
A company registration number identifies an entity in a corporate register, while a tax identifier serves the relevant revenue system. In the United States, the IRS describes the EIN as a federal tax identification number and directs newly formed entities to complete state formation first. Australia likewise distinguishes the company’s ACN from the broader ABN. Neither a number’s length nor its appearance on an invoice establishes the legal structure of its holder.
Allow for jurisdictions that connect their numbering systems
The distinction is functional rather than a rule that every country must issue unrelated numbers. Hong Kong now uses the BRN as the Unique Business Identifier for Companies Registry purposes, with mapping for former company numbers. When reviewing documents, record the issuing authority and identifier type alongside the value. Verify each number through the appropriate official service and match the legal entity details instead of assuming that one tax or registry result answers every question.