I agree that book value is tax basis, but disagree with using book value for stock value recorded on the corporation books as it is a standard accounting method to record the stock value at FMV. Most of your web research only talks about tax basis and therefore does not address the recording on the corporate books. FMV booking is especially needed where you have two 50-50 owners when one shareholder contributes cash and the other contributes property of equal value. Here is a quote on how one accounting textbook states for recording stock value on the corporation books:
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McGraw-Hill
Noncash Acquisitions
Companies sometimes acquire assets without paying cash but instead by issuing debt or equity securities, receiving donated assets, or exchanging other assets. The controlling principle in each of these situations is that in any noncash transaction (not just those dealing with property, plant, and equipment and intangible assets), the components of the transaction are recorded at their fair values. The first indicator of fair value is the fair value of the assets, debt, or equity securities given. Sometimes the fair value of the assets received is used when their fair value is more clearly evident than the fair value of the assets given.
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