The IRS uses
eins to identify entities that are required to file various tax forms. Essentially, it is equivalent to a social security number for a business.
EIN information is sourced through public filings through the Department of Labor and the Internal Revenue Service, both current and historical. Infogroup has compiled historical data since 1994.
Banks and insurance companies have express strong interest in this data for verification and authentication of a business. It also aids in looking up companies through government agencies.
eins_count- Data Dictionary