The progression of the Diagnostic Codes in Psychiatry and archaeological implications

All official diagnoses have a numeric code attached to them. It struck me a while back that there is a bit of history implied in those codes. Attention Deficit Hyperactivity Disorder, combined type is 314.01, inattentive type alone is 314.00, but hyperactive type alone is 314.01 which I suppose suggests that the original perception of the diagnosis was of something associated with hyperactivity and only later was it seen as useful to consider the criteria and make a diagnosis in the absence of hyperactivity.

Perhaps there is a psychiatric resident's progress or the fields progress implied in the mood disorder codes. As a first year resident you confront the awe inspiring threatening pellucid black cloud of Major Depression, 296.2. Getting something of a grip, you find that the patient did too but lost it and progressed to 296.3, Major Depression, recurrent. But there is more to mood disorder. Sometimes the patient might have prominent irritability or high moods and be in Bipolar I disorder, manic, 296.4. And sometimes they have been there but are in a state perhaps now indistinguishable from Major Depression but, having been to 296.4, they are now at 296.5, Bipolar I disorder, depressed. And, finally, or not, they may be having alternating or mixed states together and, no longer a child in psychiatry, you see Bipolar I Disorder, mixed, 296.6.