There were always two ways to look at that (if it was true). One just became less pessimistic, and more realistic.
1. Cayman yields were great, and most dies qualified to have all shaders enabled.
2. Cayman yields were terrible, and units were disabled on both parts. 6950 BECAME 6970 (Or at least shader specs drifted downward; perhaps revisioned more than once) allowing greater allocation to 6970.
The mill, and reality, points to number 2.
Our Chinese/Taiwanese friends supposedly 'in-the-know' mentioned long before the 6900 series release that it had (according to Googlnese) been "melted down" and changes had been made reducing shader count (From 1920 to 1792 IIRC, but I may remember wrong). I don't know exactly what was meant by that, but there was likely something to it. This is on top of reporting from a different source Cayman was taped out at least twice, the last time a pretty short time before launch (late Q3).
TechEYE also ran a post (from 'inside-Taiwan sources') on Nov 7th indicating yields were in single digits and AMD was in a scurry to get SOMETHING out to compete because enough fully-functioning dies were not going to make it for a Q4 launch. So there's the hear-say.
Then there's facts. Not only was Cayman delayed, reinforcing yield rumors, but when you start looking at performance for 6950/6970 relative to Barts things get ugly. I don't know how any other conclusion could be reached other than this compromise satiated their need for yield, performance above Barts, if only barely, and the realization these two products were the only two they would be able to harvest dies for. It's hard to believe 6950 was planned to be only 10% faster than 6870, and the two 6900-series products 10% apart. We all know the standard gap between products (~15%), and this ain't that on multiple levels. Also note not only is 6970 the first part in eons from ATi with an unorthodox clockspeed (They HAD to release something comparable to GTX570, yields be damned) but that this core was architected after they knew their direct competition (512sp Fermi, ~750mhz). When a mid-range GTX560 (upclocked, mind you, to unexpectedly compete with 6950) is coming that will destroy not only Cayman's intended MSRP, but put pressure on AMD's whole $200-400 stack when AMD typically prides themselves on efficiency, you know something had to have gone terribly wrong.
If anything, the flashing ability would likely indicate 6950 was not planned to have 1408 shaders from the get-go, or the dies WOULD be locked down from TSMC. What if 6950 was planned to have 1536sp? To me, and I may stand alone, that makes a TON more sense.
The plot thickens...
The 6990 might be the full blown 1920 shader model that we all thought the 6970 was.
