Today, scholars regard two medieval Armenian Lectionary manuscripts as intact witnesses to the worship patterns of the late antique church of Jerusalem: Jerusalem St. James Monastery Arm. 121 (J) and Paris BNF Arm. 44 (P). This article challenges this assumption. Through a case study of the Holy Thursday rubrics in these manuscripts, I demonstrate that the lineages of both were likely shaped by the same scribal interventions visible in other medieval versions of the Armenian Lectionary and that the two may be eclectic texts. The article concludes that a thorough text-critical study of the Armenian Lectionary tradition is necessary to accurately reconstruct the shifting practices of the fifth-century Jerusalem church, a study that should incorporate a wider field of available witnesses.