Reliability rating is focused on bugs, an issue that represents something wrong in the code. If it has not broken yet, it will, and probably at the worst possible moment. It needed to be fixed, yesterday
The reliability rating is calculated using the worst severity found for a bug:
A = 0 Bug
B = at least 1 Minor Bug
C = at least 1 Major Bug
D = at least 1 Critical Bug
E = at least 1 Blocker Bug
