The data shows that zo3-ded4 (做得) is the dominating one to express possibility or permission in deontic modality; the adoption of zo3-m5-ded4 (做毋得) is preferred than that of sii2-m5-ded4 (使毋得) in expressing prohibition.
the role to denote the idea of "not necessarily" falls on m5-sii2 (毋使) exclusively.