https://www.schwabassetmanagement.com/resource/2024-supplementary-tax-information shows that only 33.3% of SNVXX is in US Gov Obligations, and only that portion would be generally exempt from state income taxes.
So I wonder how you got the 99.5%.
Also, for CA/CT/NY, see the remark at the top of that document about it not meeting the minimum investment requirements to permit the "pass-through" of exempt income. :(
