Thanks for the auction link, magnarc. One of the fun things about this hobby is that just when you think you've seen everything, another oddity shows up. Never seen a gray wrinkle 604C before, but I have seen a few gray wrinkle 802C compression drivers. This is the same paint that was applied to the B series drivers. Evidently the change to the C series drivers was made just before the change to green paint. I seem to have it in mind that the C series appeared in 1952, but that may be off by a year or so.