SATB short score (voices 1+2 on treble, 3+4 on bass) is valid exactly when both same-stave pairs stay homorhythmic and non-lattice — stated as one composite boundary

Gradus's SATB grand-staff default (voices 1+2 share the treble stave with opposed stems, voices 3+4 share the bass stave with opposed stems) is the correct convention for chorale-style four-part harmony, and stops being correct exactly at the boundary defined by the preceding rules taken together.

Content authored on the SATB grand staff where either same-stave pair (S/A or T/B) trips the role-inversion threshold, the beam-lattice threshold, or is independently classified per voice-independence-metric while containing beamed durations.

Gould, Behind Bars, on SATB short score as the standard chorale-engraving convention.

This rule needs the notated content and the rendered result together — the score says what should happen, the page says whether it did.