It's not uncommon for multiple people to be involved in writing a script and different times. However, when more people get involved it often means that a script is having difficulties. This may be bad news for Spider-Man: Homecoming.
It now appears that rather than being a reboot, the new Shaft movie will actually continue the Shaft saga that's been running since the 1970s, because Samuel L. Jackson is being eyed to return. And that's just the tip of the iceberg.