While it is widely recognized that many successful artists, such as Titian, made autograph replicas of their own paintings, this phenomenon is only beginning to be studied in the work of Guercino. He started making such replicas from the very beginning of his career, since a surprising number of duplicate versions have been identified from before his Roman period (1621–1623). Repetitions made during the period of the artist’s Account Book (from 1629 until the artist’s death in 1666), on the other hand, are a more vexed issue. The debate over prime and second versions by Guercino from his mature period was reopened in 2005 with the re-appearance on the London art market of Guercino’s lost version from Northbrook Park of his 1645 composition, Semiramis at her Toilet Receiving a Messenger, first published by Denis Mahon in 1949 and now in a private collection, New York. Less than five years earlier, another autograph version of the same subject, now in the Cobbe Collection at Hatchlands Park, had come to light and was also endorsed by Mahon. This article examines the differences between the two versions and concludes that the Cobbe version of the composition (commissioned by Cardinal Federigo Cornaro), slightly less finished, was painted first.