The reason behind this is to imply that some tragic events haven't happened yet. The plot will go as it was. It might just change the way you view it.
This show is also trying to convey the message that we are not aware of what's going on in each other's lives. We just need to be there for each other and support each other regardless of what rumors we hear about them. There's too much hate in the world, especially in high school. We must overcome it and learn to appreciate each other for who we are.
Many sources like MoviePilot, this, this and others have suggested that why deposition tapes are dated November 10, 2017 implies that if this story were happening in real life, then some of those tragic events wouldn’t have happened yet.
MoviePilot suggests that everything that happened during or after Liberty High’s summer break — including Bryce Walker raping Jessica and Hannah at separate parties, Mr. Porter telling Hannah to just “move on” from her trauma like it etc had never happened.