I'm not sure I really wanted to know that, Bob, but thanks for the information anyway, I guess.I find that a cake of soap will last me several months. Even longer if I don't wash every Sunday.
I think we see the degradation of certain products happening a lot in our society today. Although another example of said degradation escapes me at the present time, I know it happens.
I'm guessing the partly-used cakes of soap that might have gone home with the cabin staff is similar to businessmen and travelers coming home with little bars of soap from the hotel. However, I don't think those have been used. It sounds like the same concept. Instead of "Hey, look at this! This bar of soap came from the Hilton," it is "Hey, look at this! This bar of soap came from the Titanic!" Anyway, I think I have finished including my two-cents worth (alas, another cliche).