Well, it must be an ultra-rare "S207", probably the only one ever produced. I stand corrected. You have a very very rare and extremely valuable knife there, a one of a kind. The "S207" is not even documented in any book, which is an indication of its rarity. In fact, (in those days anyway) Case only used "S" to indicate a handle material on one knife, the S-2, which was a small gent's lobster pattern with a patterned sterling silver handle. So the letter "S" was used to designate a sterling silver handle.
So your knife most likely is a one of a kind prototype with a sterling silver handle, which was patterned and colored to look like Case XX era red jigged bone. The use of a lower case "S" kind of throws me though, since whenever letters were used by Case to designate handle materials, the upper case letter was always used. Another indication that it is an extrmeley rare one of a kind protoype. Case must have been experimenting with the use of lower case letters, just on this one knife. They did manage to duplicate the look of jigged bone very well, though.