If the hold to maturity holdings were marked to market, it would have been apparent that there were problems. At the very least, SVB would have had to acknowledge that their holdings were not worth nearly as much as they used to be. I think the larger banks in the US are required to do this with their holdings. The FT indicated that if the US required all it's banks to adhere to the Basel III regulations instead of just the large ones, SVB would not have had the same issues either.