It’s all good observations:

Brandom does not explore subvocabularies (he focuses on examining a single pair of meaning-use relationships applied to modal logics).

Also, user’s doing comprises his pragmatic domain.

It’s exactly the purpose (or meaning) of the software design to cooperate with the user to make him express his practices (and thus build a set of his vocabularies) and then map them into “implementation stories” (i.e. given software vocabularies, what needs to be done softwarewise for the user stories to be said).