Around 2008, I read some public filings by banks. I made only two back-of-the-napkin adjustments:
1) I combined off-balance sheet assets and liabilities into the balance sheet, and
2) I changed the expected % losses to approximately that of Wells Fargo.
With those two simple adjustments, I saw that some big banks were in the hole by (combined) tens of billions of dollars.
The market prices for these banks made it clear that major investors either didn't read or didn't understand the data in the public filings.
Fun fact 1: My bank WaMu which was itself was maybe $0-$10B in the red so I immediately withdrew $2K in panic. I found that money hidden in my filing cabinet about 5 years ago.
Fun fact 2: What was even more crazy is that a famous private equity firm (I think TPG) had just dumped in billions of dollars into WaMu but that still didn't fill the hole (and why would such a big firm be less sophisticated than a nobody like me?)
Fun fact 3: FDIC had ~$50B at the time, which maybe wouldn't cover the losses at the pessimistic end of my estimates.
Fun fact 4: In accounting classes, I identified 3 very shady areas of accounting: options, off-balance sheet entities, and pensions. I believe the first two have since been fixed but I think pension accounting is still very shady so... beware.
Disclaimer: I studied finance and accounting in school and read 10-Ks in my spare time in the early 2000s so I have some knowledge of accounting shenanigans. I also had some experience in real estate. But that's about all the expertise it took.
(Several edits made to improve readability.)