The adjective problem
Many voice guides are collections of desirable adjectives: clear, human, confident, warm. The adjectives are unobjectionable and therefore weak as institutional decisions. Almost every organisation would claim them.
They do little to resolve the difficult moments: what uncertainty should be admitted, what authority should not be implied and which public obligation should govern a commercially attractive sentence.
Character before cadence
An institutional voice begins with character, competence and relationship. A court, university, bank and public-interest organisation may all value clarity, yet clarity serves different duties in each.
Cadence and vocabulary matter. They become coherent when they express prior decisions about authority, evidence and the public.
A system that survives personalities
The system should help different writers make recognisably governed choices without imitating one founder's mannerisms. It should define terminology, proof thresholds, boundaries and escalation questions.
An institution's voice is the audible form of its character. The language remains stable when the character has been made explicit.