I have no dog in this fight but I never heard of the Dick Act and so I find the topic interesting. From my 40 minutes of research starting with the Dick act that does indeed separate the militia into 2 groups here is what I conclude:
Defense acts come and go, and so doing a quick google search on "reserve militia" (able-bodied men between 18 and 45) I came across U.S. Code § 246 of 1956 which defines militia as:
The militia of the United States consists of all able-bodied males at least 17 years of age and, except as provided in
section 313 of title 32, under 45 years of age who are, or who have made a declaration of intention to become, citizens of the United States and of female citizens of the United States who are members of the National Guard.
The classes of the militia are—
(1) the organized militia, which consists of the National Guard and the Naval Militia; and
(2) the unorganized militia, which consists of the members of the militia who are not members of the National Guard or the Naval Militia.
www.law.cornell.edu
I'm unaware if this definition has been superseded by a later act. Likewise I'm no lawyer but in my layman's mind a "well regulated militia" would limit the 2nd amendment to that part which is organized and wouldn't protest if federal judges viewed it in such a way.