RSU vs RSA

One thing I struggled to understand during the internship is how to calculate Fully Diluted Shares Outstanding. Treasury Stock Method and If-Converted Method all made sense to me, but for some reason it didn't seem to make sense why we don't include RSA.

To begin with, once RSU becomes vested, the owner has to pay tax for it, whether the owner exercises or not. Typically, the owner has an option to eventually receive the number of corresponding shares - number of shares equivalent to the amount of tax payable, or to simply pay the tax in cash. The tax here is income tax for the total amount of value, not the long-term capital gain (which applies to stock options).

If RSU is not vested, it should be treated using TSM. However, there are three kinds of RSU:
1. time-based: RSU becomes vested according to the predetermined timeline
2. time-accelerated: time based, but if certain metrics are met, it will become vested
3. service-based: based on stock price, EPS, etc.

None of these methods give an exercise price. Therefore, when adding RSU, you use an exercise price of $0. Or, this is equivalent to not using TSM at all but just adding the number of RSU's unvested instead.

RSA, however, is slightly different because the stocks have already been issued, and they are already part of the basic shares outstanding. Unvested RSA just means that while stocks have already been issued, they just can't be sold to anyone. Also, both vested and unvested are entitled to dividends. So when the company discloses the amount of unvested RSA, there is no need to apply TSM because it's already included in BSO.

Another major difference between RSA and RSU is the timing of tax. RSU is always taxed at the time of vesting. However, RSA has an option to be taxed at the time of grant, should the owner choose to elect section 83b. Because of this, there is no way to find whether unvested RSA already paid for its income tax or not (I think).