The Code of Federal Regulations (CFR) is a codification of the general and permanent rules published in the Federal Register by the Executive departments and agencies of the Federal Government.. Title 21 of the CFR is reserved for rules of the Food and Drug Administration. Each title (or volume) of the CFR is revised once each calendar year. A revised Title 21 is issued on approximately April 1st of each year and is usually available here several months later.
CFR 21 was downloaded from the files of the Government Printing Office (GPO) and contains the most recent revision. The CFR at GPO, both current and historical, can also be searched directly at: http://www.ecfr.gov/.
The 19 Sept date most likely refers to the date that the website was updated, not that particular page. I say this because the same date is on the Title 21 search page as well.