If a fabric, whatever it is called is waterproof, then it's waterproof. Some, usually depending on the quality of the outer fabric are more durable than others. Rucksack straps etc can wear away a lower grade fabrics waterproof layer/coating.
However the main thing where a garment stands up or falls down is the quality of the seam taping. this is where rain is most likely to enter and will do so if the taping fails. It is not the tape exactly but how well it is adhered to the seams.
I had a waterproof jacket with taped seams that failed the first time it was worn on the rain. The taping literlay peeled off and i ended up soaked through. It was a cheaper jacket, my usual more expensive jackets have weathered many a storm without problem.