Commenting on the unreliability of Church calendars from the fifth centuries onwards and their claim that John was martyred, Sean McDowell wrote:
The Calendar of Carthage (c. AD 505) celebrates the feast of John the apostle and the apostle James, who was killed by Herod. Even though the calendar refers to John as “the Baptist,” there was likely confusion by the author, since John the Baptist was also celebrated later, on June 24. The author may have conflated John the Baptist and the apostle, since both were beheaded (Acts 12:2). In a Syriac martyrology in the East (AD 411), a celebration of James and John (December 27) is sandwiched right between the martyrdom of Stephen (December 26) and the apostle Paul (December 28). There is a Gallic tradition possibly as early as the fifth century that celebrates the martyr deaths of James and John on December 27. A similar commemoration can be found in the writings of Aphrahat (AD 344). Interestingly, Aphrahat had previously referred to the stoning of Stephen and the martyrdoms of Peter and Paul, and yet he identifies James and John not as martyrs, but as walking in “the footsteps of their Master Chris.” Why the difference? Did he still mean martyrdom?
This passage in Aphrahat raises an important distinction in how James and John have been remembered in comparison with the other apostles. While they were commemorated together shortly after Christmas in both the East and the West, it is not clear that it was because of their mutual martyrdom. In fact, Bernard argues that the tradition of their mutual commemoration began with Gregory of Nyssa (c. AD 335-c.395), who was careful to distinguish between commemorations of martyrs from apostles. Gregory recorded the crucifixion of Peter and the beheading of James, and yet with John he tells the story of the boiling oil and his willingness to suffer as his witness for Christ. According to Bernard, James and John were honored as apostles, not martyrs. James honored Christ by his martyrdom, and John honored Christ by his willingness to die as a martyr.
Even I these passages do refer to the martyrdom of the apostle John, as Boismard surmises, questions still remain as to the historical value of these accounts. Little evidence attests that those calendars and festivals date before the end of the fourth century (c. AD 400). At best, these liturgies demonstrate John’s death was celebrated at this time. Given that the tradition arises in the late fourth century, a time when tradition was often untethered to history, it is questionable how much historical value it provides or the martyrdom of John. (Sean McDowell, The Fate of the Apostles: Examining the Martyrdom Accounts of the Closest Followers of Jesus [New York: Routledge, 2015], 154-55, italics in original; see pp.148-55 for a fuller discussion of the purported martyrdom of John, something McDowell concludes is “improbable” [p. 156])