I've not seen a single clear and irrefutable example of a definite anarthrous predicate nominative before the "be" verb in apostle John's writings. But I've seen plenty of instances where such nouns CANNOT be definite in his Gospel. Trinitarian Harner claimed that the following cannot be definite in the Gospel of John: John 1:14, 2:9, 3:4, 3:6 (twice), 4:9, 6:36, 7:12, 8:31, 8:44 (twice), 8:48, 9:8, 9:24-31 (5 times), 10:1, 10:8, 10:33-34 (twice), 12:6, 12:36, 18:26, 18:35. For once, he was absolutely correct. The record speaks for itself, θεὸς at John 1:1c is not definite. The betting average is zero, or best case, close to zero.