Commenting on the use of τετέλεσται in John 19:28 (cf. v. 30), Robert Tomson Fortna noted that:
Possibly also Johannine is the choice of the verb teleiōthēi
to express the fulfillment of scripture in the next clause; it is a cognate of
the term [the Gospel of John] inserts both here in v. 28a and again in 30. (Robert
Tomson Fortna, The Fourth Gospel and Its Predecessor: From Narrative Source to
Present Gospel [Edinburgh: T. & T. Clark, 1988], 185 n. 426)
Further Reading:
Full Refutation of the Protestant Interpretation of John 19:30