In fact I think I was the first to do a hidden pocket. I did one in 1991. The customer asked me to make a hidden pocket large enough for a kilo of sugar. I am not kidding those were his exact words.
So I made the case extra long and the lower outside pocket had a false bottom and under that was the hidden space. If one were to unzip the upper pocket then the hidden pocket was completely undetectable. You had to know just how to reach in to remove the false bottom. I am sure that the owner was able to satisfy his sweet tooth.
And recently I made a hidden space in a case like this:
Just enough space for a tip tapper or whatever else might be about that size.
Cases that I am missing are Whitten (had two previously), New York Case, Melton, MAT, Jim Knott, Waldemar Eisele, True West, My Personal Instroke that I made for myself and lost gambling, Centennial (had one) Ann Gore (had two), Evladin, AVP and Harvey Martin.
I am sure I forgot some others. Eventually I'd like to collect all the current case makers' work and hang them up like art. But Karen disagrees with me and thinks that vacations and stuff for Jessie are more important. ;-)
In fact she would be happy to sell all these and apply the money towards those things.