I would say that what doesn't happen today, will happen in the future. If a part of your application is critical enough that you wrote 100 tests already, then you can add a few more edge case scenarios, it won't hurt. Those edge cases will happen in pro, sonner than you can imagine. 0.01% of probability when used by thousands of people will break the statistics lol.
If your deadline is too short, you need to argue on that matter, but if you can handle a few more cases, it's better.
Better to be ready than sorry.