Mid-1990s-present - US and Non-US companies - Online
"The SEC’s EDGAR database provides free public access to corporate information, allowing you to quickly research a company’s financial information and operations by reviewing registration statements, prospectuses and periodic reports filed on Forms 10-K and 10-Q. You also can find information about recent corporate events reported on Form 8-K but that a company does not have to disclose to investors..."
Mandatory electronic filing via EDGAR began in the years 1993-1995.
Read more about EDGAR on the SEC's web guide Researching Public Companies: A Guide for Investors.