Complex sentence: The first known edition of this work was published in Seville in July 1510, but there was undoubtedly one prior (perhaps published in Seville in 1496), since the sixth book of the series, "Florisando", appeared in April 1510.
Split into simpler sentences: The first known edition of this work was published in Seville in July 1510. But there was another edition published prior, possibly in Seville in 1496, as the sixth book of the series, "Florisando", appeared four months earlier, in April 1510.