Mark to market for bank capital adequacy and Rick exposure can and sometimes does differ materially from GAAP. Specifically, measures such as probability of payment (pop), loss given default (llgd) are used in risk asset classification in bank examination but not used in that way in GAAP. Similarly liability risk has rate, liquidity and valuation components in bank assessment that have no direct counterparts in GAAP. That is why all this tends to be referred to as CAMEL ratings. These are obscure but nit secret just as bank consent decrees are not technically secret.
These are some reasons why SVB was NOT a surprise, nor was Signature. People who watch that tend to avoid discussing this unless a bank fails because poor CAMEL ratings can be and usually are repaired without failure. Failures, though, do usually happen with warning if only people were paying attention.
. 
