They are not centered any better or worse than the Toshiba parts, or OnSemi that I’ve seen the innards of. The size of the clearance hole in the leadframe isn’t critical unless it’s a 1500V horizontal output type (which no one uses anymore). If the epoxy seal is good right up to the die there ain’t no water getting in. It’s got further to go from the mounting hole anyway than it does around the base and emitter leads. One can often tell fakes by the “wrong” size hole in the leadframe, compared to what a given manufacturer normally uses. But that doesn’t mean a different size is bad. Just not right for Toshiba specifically.
