MVNO opacity

MVNO opacity is the reduced visibility of carrier signals for numbers served by mobile virtual network operators, resellers who run on a host carrier's network. Signal APIs often see the host network's view, not the MVNO's subscriber records, so SIM changes and ports on MVNO lines can be invisible or delayed. Honest identity systems treat MVNO coverage gaps as a no-answer, not a pass.

The failure mode this creates is silent rather than loud. An API that answers 'no swap detected' for a line it cannot actually observe is indistinguishable, to the calling code, from one that checked and found nothing. Treating the two as the same value is how a coverage gap becomes a false pass.

The remedy is to carry the distinction in the response and in the rule: a missing observation belongs in the same branch as a provider error, which is the branch that falls through to whatever check ran before the signal existed.

Sizing the gap matters as much as handling it. In markets where resellers hold a substantial share of subscribers, a signal that cannot see them is not a minor caveat, and the share differs enough by country that a control validated in one market can be much weaker in another without anything in the code changing.

The measurement that reveals it is a coverage rate rather than an accuracy rate: of the lines checked in the last month, what fraction returned an observation at all. That number is rarely reported by default, and a system that does not compute it cannot tell a quiet month from a blind one, which is the monitoring version of the same failure.

The remedy is cheap where it is designed in and expensive where it is retrofitted: one extra state in the response type, carried through to the rule, versus an audit of every call site that assumed two states. Deciding it at the point the client is written is the difference.

The same distinction between a checked line and an unobservable one governs how SIM swap detection should report its result.