It has been know for quite a while that Apple using a few different sources for there screens and other components. To not do it this way would mean more line shut downs waiting for parts. It does not mean that there is a 50% failure rate. It does not even mean that 50% of the screens differ. Ideal they should be impossible to tell the difference, but the different manufacturing it is inevitable the there will be a difference now and again, and that is not saying the the difference is bad. I would be curious to see the screen part numbers on these machine the OP was talking about. I do think some of it just happens to be people messing around.
Until recently I worked in the semiconductor industry and there was a well known client that only purchased through us. We had a problem in the manufacturing process that was able to pass through all of our testing and it shut down their line for almost a month. I can not mention who they are because even though I don't work there anymore I am still under the company confidential clause, but they are a well known tech name. When possible companies will have a few different vendors to prevent shut downs.
Your correct with what your saying in the sense that having only one vendor could cause manufacturing delays. However, with Just In Time manufacturing that has always been an issue because no one then wants to inventory anything. But for years there have been many Lean Manufacturing techniques available that could provide for a cost effective and less risky means to maintain a specific vendor for a particular panel. Like customer KanBan on the floor along with point of use inventory. If your familiar with these concepts then you know what I am talking about and for those who are not, this is where the vendor agrees with the manufacturer to continually supply a buffer of a part on the floor, such as the lcd, and when the KanBan level reaches the set threshold minimum quantity, the vendor replenishes it. Therefore always ensuring enough inventory to keep manufacturing flowing. This also provides other benefits such as better pricing due to long term larger quantities and allows the vendor to "tool up" for larger runs and then feed them to the KanBans within a set schedule.
Now Apple could easily work out a KanBan agreement with some of these panel manufacturers if they wanted to maintain a single model screen and ensure consistency in their end products, then have a backup vendor only as contingency with its own Kanban to ensure product is always available in the event of an emergency. Then the end users would only see a different vendor screen in their MBP in very small limited instances. only when there is a rare issue with the primary chosen vendors product.
I believe the reason Apple and other manufacturers don't use these techniques is because they truly want to the manufacturing to flow constantly of course, but they also have a primary objective of LOWEST COST vendor products. This means that having multiple vendors and using them against each other in an effort to win Apple's business in larger quantities, it usually ends up in a mini bid war where the vendors try to underbid each other resulting in lower cost to Apple.
This to me is an archaic and non-value-added practice to what should be the most important part of Apple's success, THEIR CUSTOMERS. But alas, nowadays it isn't customer who matter one bit, only stockholders.
Please don't get me wrong and think I am picking on Apple because I am not. I actually really come to love the company in many ways. They are practicing what the majority of manufacturers out there do, I just wish they would see the real value in the Lean Manufacturing approaches that truly work and every wins.
BTW.. I think the whole 50% screen thing mentioned by the original poster has been mis-interpreted along the way. It is my belief he meant that basically half the screen he was seeing were different from each other in image quality. Not that they were defective as would be dead pixes, vertical lines, etc. To me I understood it that way anyhow and I also would expect it when at least three different vendor LCD panel designs are being used in the same MBP model. There is going to be a difference as you know.
Probably the best thing people looking to buy a new machine can do is to go into the Apple Stores or call Apple sales and ask how they can ensure they can buy a machine with the desired lcd model. Of course Apple can't really accommodate this but they will at least be hearing the voice of the customer and realize that panel "A" or "B" is most desirable to their customers and it may just help Apple try a little harder in dealing with that particular vendor as a preference. Anyway just a thought. Good luck to all in the great screen lottery
