For the 1099-INT, the US Treasury obligations show in box 3 of the 1099-INT form, so there is no follow-up question needed for $$ showing there.
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I have Fidelity SPAXX too, and my Supplemental information sheets show that those $$ are only being reported on box 1a of a 1099-DIV form. (Added to whatever else you may have that dumps $$ into box 1a of the 1099-DIV). I don't think any of the SPAXX $$ end up on a 1099-INT.
The supplemental sheets only show the details on what went into the main 1099-INT or -DIV forms that show on the first page of their consolidated tax reporting PDF sheets.
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
