The publication of the Missale Romanum (1570), revised at the behest of the Council of Trent (1545–63), had direct consequences for plainchant. In order to celebrate a sung mass, the contents of graduals had to be brought into conformity with the new missal. In 1572 the Venetian firms of Giunta and Varisco issued the first printed editions of the Graduale Romanum in Italy after the missal’s promulgation. The volumes contain prefaces adumbrating the requisite alterations, which from 1580 onwards were mostly assimilated into the contents of subsequent graduals. Three types of modifications affected chant melodies: the removal of text, the addition of text, and the addition of new propers. This study explores these categories in key editions of the Graduale Romanum printed in Italy between 1572 and 1653. Analyses of five offertory chants reveal that the combination of editorial freedom, source interrelation, and textual variants in editions of the Missale Romanum resulted in musical diversity. The removal of text in the offertories Iubilate deo omnis terra and Iubilate deo universa terra reflects the editors’ aesthetic preferences and their understanding of musical grammar. In Dextera domini and Iustitiae domini, the addition of text is dependent on the edition of the missal used in the process of collation, the relationships between the sources, and the editors’ responses to the changes mandated. The added chant Insurrexerunt in me, with its mixture of traditional and contemporary characteristics, highlights the freedom with which the editors sourced, or even composed, chant melodies. These findings highlight textual and musical diversity within newly regularized liturgical structures and clarify the relationship between the Council of Trent and plainchant revision. As a result, they call into question the suitability of the “Post-Tridentine” label often given to early modern chant.