This counts IGMPv3 IS_EX type membership reports, the report type declaring a receiver wants traffic from a group excluding only a specific, listed set of sources, the inverse filtering mode from IS_IN. An admin seeing a high proportion of IS_EX relative to IS_IN reports on a service expected to use tight source-specific filtering would recognize that clients are using the more permissive exclude-mode filtering rather than the tighter include-mode the admin intended, suggesting client configuration doesn't match the network's SSM design. A predominance of IS_EX reports where IS_IN was expected would be a configuration mismatch worth chasing down at the client or receiver level.