The AIA version of 102 (a)(1) essentially states that a person shall be entitled to a patent unless the claimed invention was patented, described in a printed publication, or in public use, on sale, or otherwise available to the public before the effective filing date of the claimed invention.

If the same subject matter in the application was known about somewhere else, then it's not patentable.  That's because it's not new or what the PTO likes to refer to as novel.

Under the AIA version, the date of the invention is not the relevant factor. Instead it's the effective filing date of the application that matters.  This version also leaves out the non-public sales activity.

The second part to paragraph (a) of AIA (subsection 2) states that the subject matter in the patent application may not have been involved in another issued patent or patent application filed prior to the effective filing date of the application that names another inventor. 

So if Joe files a patent application on Jan 3, 2014 that claims the same invention disclosed in a patent application filed by Jane on October 1, 2012 then Joe's invention is not novel.