A valid numbering pattern does not prove a number has been assigned, is active or can receive calls.
Possible length
A parser can first tell whether a number has a plausible length for a plan.
Valid range
A metadata library may recognize the range as assignable under documented rules.
Actual service
Assignment and reachability require a separate verification process. Do not label a syntactically valid number “active.”
Four checks that should not collapse into one
A number can pass a syntax or metadata check while remaining unassigned or unreachable. The Ofcom-listed UK drama example shows why plausible structure is not an active subscriber.
Possible
Question answered: Is the length plausible for the plan?
Still not answered: Does the range exist?
Valid in metadata
Question answered: Does it fit a recognised range/pattern?
Still not answered: Is it assigned to a subscriber?
Assigned
Question answered: Has the number been allocated for service?
Still not answered: Can it receive a call or message now?
Reachable now
Question answered: Can the relevant service reach it at this time?
Still not answered: Will it be reachable later?
These are conceptual evidence levels, not tests performed here. A successful prefix match in the homepage demo is not even a full-number validation result.