some things do not make sense.
Assuming you are correct that you had 3,372 A shares then your tax basis in each A share would be the $25,000 you paid for the convertible note divided by the 3,372 equivalent A shares or about $7.41 per share. Per the 8937 income is the lesser of a) $21.78 minus the basis in one A share ( $7.41 ) = $14.37 or b) $10.89. thus your income would be $10.89 times the 3,372 or about $36,721. this is more than the $35,795 on the 1099-B. I would think the 1099-B represented the actual net cash you received - don't know if any fees or charges were taken out.
then the basis in each .39673B share is the tax basis in one A share of $7.41 less $10.89 this is a negative figure and therefore not possible.
for one A share cash of $10.89 + 0.39673 shares of B (at $27.4432/share) this probably was only an estimate if it was issued before the exchange was complete. If I'm right that those were estimates, then the number of shares would change on the effective date so you got $10.89 worth of shares.
you may want to check B's investor relations website. there may be more info there or call.
I would think, which means I'm not sure, that the boot (cash) would be fully taxable (no cost basis) and the B shares now have the $25,000 tax basis of the note. future stock received would not be taxable - just more shares to split the tax basis over. any additional payments for the exchange would be capital gain. dividends would be taxable to the extent B has earnings and profits. you would be notified if any portion was not taxable.
