The day of Pentecost was 50 days after Resurrection Sunday so how does John manage to speak of the coming of the Spirit in his gospel account (20: 19-23)? Are these two accounts to be harmonised somehow are just recognised as contradictory? I wouldn't accept either of these approaches. Both are concerned to bring everything in the Scriptures under the rubric of historicity when the Scriptures evidence in many instances a lack of concern for historical exactitude. The Scriptures were not primarily given to tell us about history. They are intended to "open the mind to the salvation which comes through believing in Christ Jesus" (2 Tim 3:15, Phillips). To understand both St John and St Luke's differing accounts, we would have to examine their different renditions of the coming of the Spirit in the context of their gospel accounts. Despite the differences in timing, both connect the coming of the Spirit with the mission of the church. According to one writer , John's ...
we look not to the things that are seen but to the things that are unseen --Paul, Apostle to the Gentiles