One thing to watch as you read John is to notice Nicodemus every time he comes into focus.

Watch him move from casual observer to member of the burial party.

Watch him go from night time visitor to potential daytime follower.

Something happens with him for sure. I speculate that he becomes a follower in the new church and is used in John to show the progression – the “how” – and then to validate his story to others. Again, speculation, but not far-fetched.