In one aspect, a method includes receiving a first portion of query fingerprint data representing content transmitted by a content-distribution system. The method also includes detecting a match between the first portion of the query fingerprint data and a first portion of reference fingerprint data representing a modifiable content-segment. The method also includes after detecting the match: (i) receiving a second portion of the query fingerprint data, wherein the second portion of the query fingerprint data is different from the first portion of the query fingerprint data; and (ii) detecting a mismatch between the second portion of the query fingerprint data and a second portion of the reference fingerprint data representing the modifiable content-segment, wherein the second portion of the reference fingerprint data is different from the first portion of the reference fingerprint data. The method also includes responsive to detecting the mismatch, performing an action.