Chapter 49, Military Selective Service (50 U.S.C. 3801 et seq.) [Formerly 50 U.S.C. App. 451 et seq.]
Explanation of Change to 50 U.S.C. 3801 et seq.
As quoted from the Office of the Law Revision Counsel's website, the change occurred on December 1, 2015:
"After 75 years, the Office has decided to transfer the general and permanent provisions now in the Appendix to their proper subject matter title within the Code (predominately title 50). The Appendix as it existed prior to its stimulation can still be accessed in prior versions of both the online and print Code."
For the full explanation, see the link: http://uscode.house.gov/editorialreclassification/t50a-elim/index.html