According to the March 23, 2013 letter:
"This Fast Letter (FL) explains the changes resulting from sections 504 and 505 of Public Law (PL) 112-154, which became effective on February 2, 2013. The PL amends 38 U.S.C. §§ 5103 and 5103A to streamline the Department of Veterans Affairs’ (VA) duty- to-notify and duty-to-assist responsibilities. This new law applies to VA’s notification and assistance obligations on or after February 2, 2013. No rework of claims handled prior to the date of this letter will be required as a result of this amended law."
"Compensation Service is in the process of amending 38 C.F.R. § 3.159 to comply with this statutory change and the revisions will not be final until a later time. However, Regional Office (RO) and Pension Management Center (PMC) employees must implement key provisions of this PL immediately per instructions contained in this letter. Compensation Service and Pension and Fudiciary (P&F) Service will make necessary changes to M21-1MR, training materials, electronic systems, etc. subsequent to the final regulation change."
The full text of the FAST letter is at: