There are typically two valuations of private companies. The "internal valuation" is usually the valuation of the common shares (ie, those that are granted to employees) whereas the "external valuation" is the value of the "preferred" shares that investors purchase. The external/preferred valuation is usually higher because the preferred shares have more attractive terms (such as that you get your money back first before other equity holders are paid out).

From the article: "A 409A valuation is an independent estimate of a startup’s fair market value often used to price stock options to employees."