That is something you will notice in various solution. It is just a safe redundancy to make sure there is no runtime or logical error. The most used example that I have seen is when the author creates an array a[N], where N would be 2e5 + 10. Although, the size may never exceed 200,000. It is just there to make sure that any unexpected error does not appear.

In this case, it does not matter that we check for 82 and 83. It is just there. If you observe other submission for same problem, you may find many using x to x + 100.

First, thank you for such great contest. Truly enjoyed the questions! Did you mean that the test case 21 was added after contest or during contest?