[old_tv_nut]

Difficulty in quality control is a very reasonable speculation. Unlike later color films, in which the stages after development were driven to completion, Kodachrome had multiple stages in which hypothetically one layer could be driven to completion at a time, but practically they could not because the process would start to affect other stages. The last Kodachrome I shot and had developed at Dwayne's (for comparison to digital) has always looked to me like not all the silver was removed, although I can't prove it.

However, improper processing of film usually results in staining over time from residual chemicals rather than fading of one dye layer compared to the others. It's hard to imagine a mistake that would selectively affect the life of just one or two dye layers, but maybe.

Question: how are the blacks in your images? If they are still black and not colored, that indicates staining rather than dye fading.