If you assume that the attestation is fabricated, there's really no reason to talk about treasuries - might as well assume they embezzled 50-70B. Personally, I think it's mostly accurate, with discrepancies being around things like marking securities to market. (Just look at VC practices there, for example.) The explicit statements of "X amount of treasuries under Y maturity" are likely to be true, a vague catchall like "other investments" not so much, which puts an upper bound of ~ 15B short.

Lastly: a temporary liquidity crisis that drives USDT down far below the peg is something that would be incredibly profitable for the operators. With perfect information, it would be a situation of trading 50 cents for dollars, and could be used to erase a partial deficit overnight.