If mother nature's products were produced in a factory with exactly the same inert raw materials, and exactly the same assembly method, then the product would be exactly the same. If these factory produced products were given the exact same conditions of growth, there growth would be exactly the same.
Do ANY of these things ever happen in nature? ABSOLUTELY not!
It's human nature to try pigeonhole everything into its neat and tidy, perfect place in the world. This simply doesn't happen in nature.
May I present an analogy?
All these things that you expect to transpire on your own timetable are just not applicable to mother nature's timetable. Nature is not under your command, and there is a myriad of variables that influence the processes of nature. Do you expect every mother's pregnancy to be exactly 90 days 9 months? Under your assumptions, premature births would never occur, nor late pregnancies, nor miscarriages. Down Syndrome babies would be non-existent, etc. etc.
So when you say, "not sure how something the exact same can come up entirely different", that's just it right there: they are NOT exactly the same. You are just fooling yourself into believing that they are.