“Not Zayd but ʿAmr” expresses correction or replacement; “Not Zayd, however ʿAmr is here” introduces contrast; and “Zayd or ʿAmr” presents alternatives whose operation depends on context.
The particle bal does not automatically undo a legal effect already established by an operative utterance. Admissions and performative declarations require particular analysis. Similarly, aw does not normally make both alternatives jointly required merely because both are mentioned.
Lexical meaning is only the first stage of interpretation. Admissions, agency arrangements, and divorce statements must be read as the kinds of legal utterance they actually are.