The only way to totally duplicate it is
Same grain bill
I think all of these play into the finished product.
Hmmm. I brew the same recipes over and over. There are differences between each batch.
There may be differences in the maltster, although I'm pretty consistent on where/what I buy. The hops may not be from the same harvest. Pitching rate is pretty consistent, fermentation temp is pretty consistent.
It is difficult to produce homebrewed beer that does not have some batch to batch variability. Duplicating someone else's beer I would have to say is nigh impossible.