As has been stated, if the overlap is slight, you will never notice. The reason you see overlaps on joysticks intended to be switched (or having the capability to be fixed in one or the other) is that what makes a great diamond restricted 4-way, will also make a so-so 8-way with square restriction...and vice-versa. Some compromise is necessary with these types of sticks, or switch adjustment along with the change of the restrictor.
Perfect 4-way operation and perfect 8-way operation can't, for practical and physical reasons, co-exist on the same stick. It doesn't mean sticks which do both aren't good, just that expectations have to be tempered with what is possible, given those limitations.