From what I’ve read, they would have to mark the portfolio to market (i.e. report its value in terms of current market prices), not say “we intend to hold this to maturity” and account it at face value. Like, the latter actually makes more sense to me, but only if you actually don’t need to sell which might be true for a university endowment (all assets, no liabilities or at least very predictable liabilities) not for a hedging institution.

Wouldn’t it have just made them insolvent earlier then? How does it actually prevent the problem?

Not necessarily, since the gap in finances accumulated over time. They would have had to acknowledge asset price drops on their balance sheet much sooner. Basically they were allowed to build up a bigger integration risk with their accounting if they ever did have to sell due to not having to MTM in the mean time.

Was the accumulation duration larger than the regulatory mark-to-market period? As I understand it, SVG was heavy on US Treasuries, which lost a great deal of value due to recent interest rate hikes. As a result of a higher than expected deposit withdrawal rate, SVG sold US Treasuries for less than what they would have received if they had held them to maturity.

If the gap in finances was discovered earlier, would they have just converted more equities and other long-term higher-yeild instruments into treasuries and then go under because they couldn't get returns to match their deposit interest rates?

Had they been marking their holdings regularly they would have sold their depreciated holdings sooner when losses were smaller, instead of waiting until they had to to cover withdrawals.

Deposit interest is not fixed so that wouldn’t make them go under, they’d have to reduce their interest paid.

Requiring that they provide more information earlier encourages them to behave more safely (by exposing them to scrutiny backed by sound evidence). And if they still go down, at least it happened sooner and there are fewer depositors to be harmed.