> The two obvious examples

Appreciate this rincebrain. Know that you know better than most and this certainly covers my 2nd point. I don't imagine these cases cover my first point though? These are not bugs of the type a fsck would catch?

A fsck could pretty readily notice and repair the spacemap inconsistencies - zdb already generates its own spacemaps and compares to reality on import.

If you have the keys, technically nothing stops a fsck from noticing the encryption problems, but yes, usually it wouldn't unless you had some known issue you added special detection for, like when XFS years ago had problems with if you mounted it with inode64 once and then not the next time so the inode numbers would wraparound.