Just in case anyone was wondering, here's the answer to my question;
In 2011 Campagnolo ditched the classic 2 piece chainring bolts. The 2011 to 2015 chainsets have a threaded inner ring into which the chainring bolt screws. The big difference is that a step in the diameter of the 4 chainring bolts was removed and the diameter of the hole in the 5th pedal arm bolt changed. The profile of holes in the chainrings match the newer bolts, the cranks themselves did not change. The machining of ramps and pins on the 50T is pretty much the same, only 2 small indentations pressed into the ring a few teeth before a ramp pin.
Out of the box - no they are not compatible.
With a little bit of metalworking you can make an EVO ring fit the old chainring bolts;
- drill out pedal arm chainring hole to 10mm and you can either live with the chainring bolts sitting 1mm proud or drill out the other chainring bolts holes to 10mm,
or, if you are really good you could machine down the step in the chainring bolt or if you are really lucky find another chainring bolt that fits in your spares bin.
...a not quite engineering drawing may / may not show the difference;
I have found a nearly unused second hand set of 2014 EVO rings - ran them this morning - all good - a quiet drivetrain with snappy front ring changes...