There is no guarantee of exact same parts when getting different brands from the same factory.* All bulbs are produced at the same factories. It does not matter what brand or make. There are a limited number of factories making HID bulbs. Unless you bulb is made in North America, then it's made at the exact same factories, using the exact same parts, by the exact same people making the ones shipping free with light kits.
If you've worked in the mfg industry you'd be aware that each customer has their own specification. The parts may be exactly the same, except the gas/elements in the arc-tube are different. Even different arc-tubes and glass thickness/mfg can be used.
Cheaper solder... shorter annealing times... cheaper steel/metal parts, made on the same machines as their stronger, more expensive brothers?
There are literally thousands of different ways a company can save money on their product... while having it mfg in the same plant as other products of the same sort, on the same machinery, by the same people.
Stay Safe!