A stock index fund, or mutual fund, is a continuous offering
Huh?
A company is authorized to issue and sell a certain number of shares of stock. An initial IPO sells shares to the general public. They don't keep on putting additional shares out there. That would have the effect of diluting earnings per share and that's the last thing a company wants to do! In fact, if you read the financial pages, a lot of companies - such as Apple - are actively buying shares back. They're cash rich and this is one way they can bump up earnings per share.