A case moves through a fixed sequence, and the sequence is the control. Each step is taken by somebody who is entitled to take it, and several of them cannot be taken by the same person.
The case journey
Who hands it on, and when
Accepting a submission and giving it to a reviewer are two acts, and both are the case officer's. Acceptance says the file is complete and starts the clock; it names nobody. Assignment names the reviewer, and that is what moves the case into assessment — until it happens the case is accepted, the clock is running, and nobody has it. The screen says so rather than leaving it to be inferred.
An officer picks up a case nobody holds. A case somebody already holds is moved by the holder, or by a third officer — taking a colleague's case for yourself is refused, because that seat carries acceptance, the clock and the choice of reviewer.
From there the case is the technical reviewer's (an assessment lead may take one too — the senior variant of the same role, not a separate queue). A case can change hands afterwards for workload, absence, or a conflict found later, and every movement records who moved it, to whom, when and why. "Reassigned" with no reason is unreadable at exactly the moment somebody needs it: a case that moved between officers days before a decision is either routine or the most interesting fact in the file.
Why the clock starts at acceptance
Receipt is not acceptance. If the clock started when a submission arrived, an entity could start the Office's statutory period running by sending an incomplete file, and the Office would spend its own time chasing documents. It starts when the Office accepts the submission as complete — and a request for information pauses it, because time spent waiting for the entity is not time the Office has had.
