For example, if a company has 1,000 shares in total and you own 200 of them, you own 20% of the company.

Not really true. Most private corporations have more than one type of shares, and this article doesn't seem to recognize that. That's a huge issue.

You need to look at the articles of incorporation, the bylaws of the corporation, any unanimous shareholder agreements (Normally called a "USA"), and maybe even the resolutions in the Minute Book. Retractable, non-voting shares that you aren't allow to transfer/sell without a director quorum, are not going to get you the same as voting shares, or preferred shares, or even shares that have different transferring restrictions.