There are a lot of pattern inconsistencies that are overlooked because they're minor and/or not obvious. Working patterns are made from a master pattern, so those differences are propagated to them and exponentially to the cast pieces. The difference in the #5 could be just that, or if it was intentional, which I doubt, perhaps it was a visual reference for help in choosing a size of pan from a stack of skillets with no size numbers on the tops of their handles.