Those WinJS files are becoming quite an information leaker, and what's so great about those WinJS files is that they come directly from Microsoft themselves. Today, we have concrete confirmation that Windows 8.1 build 9600 has been compiled on August 21st 2013.
The full build string reads 9600.16384.winblue_rtm.130821-1623, this differs slightly from the recently rumored build number 9600.16384.winblue_rtm.130822-2140. The queston we must ask ourselves now is "is this the actual Windows 8.1 RTM?"
Until we have an official announcement from Microsoft, or leaks from trusted sources, we can only speculate on what this build number actually means. We do know that 9600 is going to be the official RTM, but what we're waiting for is to see if Microsoft change the 5 digit number.
Right now, Microsoft are testing build 9600.16384, and if all goes to plan, it will be signed off and sent to OEM's if it hasn't already. However if Microsoft do find a fault with it, it will be recompiled at the same build number, but different 5 digit number, and that build will be sent to OEM's.
It's entirely possible for the build string above to be 'the' RTM, but as we said, until we have some concrete information we'll have to just speculate. Check back at WinBeta.org for more news on the Windows 8.1 RTM.