Treasury Stock Method for Diluted Shares Outstanding

Hi,

I've run into a technical question someone might be able to answer: I'm currently completing online training and I've seen two conflicting methods to calculate Diluted Shares Outstanding. In a modeling exercise, diluted shares outstanding were simply being calculated by adding the number of in the money options to the number of shares outstanding.

However, in a public comps, the instructor used the Treasury Stock Method (assumes options proceeds are used to repurchase stock) to calculate Market  value of equity.

Is there a reason why the Treasury Stock Method is not being applied in a modeling forecast?