Huggies.. Wow

Not quite sure how huggies makes to separate size 5? I have been using the brand since my son started wearing diapers he is now a size 5.. 15kg plus. I need a logical answer. As I have purchased a pack of huggies 5 at pick n pay Chatsworth. And it looks relatively smaller then the other size 5..as I have a few left from the last pack.