When Danny is visiting his family's graves, his own headstone shows "199" on the right side where the date of death usually goes. If this show takes place in 2017 when it was released, it would not be possible for him to have died in the '90s at all. It was said multiple times before that he was ten when they disappeared, and that he has been gone for 15 years, making him 25. That would make the hear he died 2002.
The black student in the dojo. His belt is tied incorrectly. However it is clear from the attitudes of the students that it is not a strict dojo and as such the lax clothing is in keeping with this.
When Danny goes to visit his family's memorial and touches his mother's stone, it can be seen moving, revealing that it isn't really made of stone.
At 48:21 during the fight scene in the ring, on the background is possible to see the cameraman legs. The ring is supposedly closed, with no one else inside.