In one aspect, a method includes identifying a group of multiple content-presentation devices that are tuned to the same channel and that are each scheduled to perform, at a modification start-time, a respective content-modification operation that comprises modifying a modifiable content-segment in connection with an upcoming content-modification opportunity on the channel. The method also includes determining that, after the modification start-time, at least a subgroup of the group of content-presentation devices have detected a mismatch between reference fingerprint data representing the modifiable content-segment and query fingerprint data representing content received by at least the subgroup of content-presentation devices. The method also includes determining that at least the subgroup of content-presentation devices are connected to tuner devices associated with the same content distributor and, in response to determining that at least the subgroup of content-presentation devices are connected to tuner devices associated with the same content distributor, performing an action.