Oh they get cloudy. My old 50mm collapsible Summicron (1954) was so cloudy when I bought it you couldn't see through it. As somebody mentioned above, it's probably due to outgassing of the lubricants. The good news is that most haze is easily cleaned. I had my Summicron cleaned and it's now one of my favorite lenses. As to when the fogging stopped, probably in the 1960's I'm guessing, though you can argue that it's probably still going on, if the outgassing theory is true.

Jim B.