I have decided to take over an open source (MIT license) project that hasn't been maintained in 4 years, but I want to maintain it on GitLab (as opposed to current GitHub). I have decided NOT to fork the project, but instead clone it and rebrand it and publish it under a different name. Even though this is generally frowned upon, the reason is that I also plan to make extensive breaking changes to the code and alter its API surface substantially and I do not want to mess with existing user base but instead offer them a documented way to modify their projects if they want to. So there would never be any future upstream or downstream changes to or from original project.
Now comes my conundrum. The project contains MIT license which I plan to fully honor and inherit, and MIT license mentions only the original author. For start I intend to implement changes as per answer on "If I fork a project on Github that is licensed under MIT, how do I handle the attribution and copyright notice?".
However, aside from him, there are about a dozen contributors whose code is part of the project. I will preserve the original git history, so they are all mentioned in the git chain, but I need to know if I am required to list them all now in my MIT license? Especially since only one of them has GitLab account, the rest are just listed in contributors section by nick/email (on GitHub its easier because they are directly attributed on the project page). Did the original author make an oversight by not including them in the license file?