If your premise is that the ONLY way to have a new MA System is to have new patterns, then your premise is faulty. You can codify a new system through technical parameters for fundamental techniques. Take stances for instance as one element. Codifying length, width, angles of feet, weight distribution, amount of knee bend etc. Once you codify technical parameters, you then develop patterns containing the fundamental techniques. According to General Choi's Bio, this is what he did creating the "foundation" from 1946-1955. This also follows how he wanted TK-D taught, teach the fundamental techniques that are new to a pattern before teaching the pattern, and also how his 15 Volume set is laid out with Fundamental techniques in earlier volumes, patterns in later volumes with each pattern section being preceded with details about each new / additional technique not performed in earlier patterns.
Your "Mid 50's" no patterns point is moot since "Tk-D" wasn't born until the the mid 1950's (1955) or so and no one claims it sprang from the womb fully formed.