Rather than start up yet another IMS bearing thread....
I've read through all the arguments and theories in this thread. I'd like to add one more that hasn't been discussed at all.
It's known throughout the ball bearing industry that there's a lot of counterfeiting going on. Cheap bearings are marked with "brand name" markings such as from SKF, Timken, et al. The counterfeiters are very clever at making both the bearings and the packaging look identical to the real thing. The only difference is that the fake counterfeit bearings simply have a short working life.
Porsche uses NSK brand bearings for the IMS bearing. However, NSK experienced a rash of counterfeit bearings in the German market just about covering the time frame of the IMS bearings at issue.
Product: Resolving of counterfeit problem | NSK
I wonder whether Porsche got a percentage of counterfeit NSK bearings in from suppliers. IIUC the IMS with bearing already installed is received as a complete subassembly from Porsche's suppliers, so Porsche doesn't directly buy the bearings from NSK. A random scattering of counterfeit NSK bearings would explain the somewhat random failures of IMS bearings. There have been many theories proposed as to why certain cars experience IMS bearing failures and why others survive to a ripe old age. Counterfeit bearings could be one significant reason. Porsche engineers may have correctly designed the engine when genuine bearings are used, but did not anticipate inferior counterfeit bearings entering the supply chain.
Guys like Jake Raby have examined thousands of IMS bearings, but it would be interesting to see if even he could tell a genuine bearing from a fake counterfeit part.