I'm starting this thread to help track PowerTap versions. CycleOps has a history of undocumented and opaque revisions, especially with their pre-built wheels at Performance Bike. I bought a wheel and Little Yellow Computer in 2005, and I only knew that it would be a PowerTap Pro because other forum users had posted about it.
I got the PowerTap Pro wheelset at Performance at the end of May, manufacture date April 2013. The description online lists a 2032 battery. The User Guide (21476, 10/12) is a combination of the 07/11 User Guides available at http://www.cycleops.com/pdfManuals/: G3/G3C (20373D) for most and Pro (20374D) for table of measurements. The end cap is the PowerCap with removable electronics and 2032 battery. The Pro 70.0mm flange diameter appears correct on rough measurement. There is a blank ring around the PowerCap: it appears to be retrofitted into a Pro hub shell.
The confusing thing is that the Pro had already been redesigned for late 2011–early 2012, coincident with the G3 introduction, with a lighter shell and 2011 SL+ internals (2 x 357 batteries in a holder). All the photos I have found at online stores show the old end cap if visible (the Performance photos are from the freehub side). I find it somewhat implausible that all these stores are still holding inventory of the old version.
The PowerTap rebranding last month will probably add yet another revision, although the omission of the Pro might indicate its discontinuation.