The 6870/50 were launched on October 22nd and the 6950/70 arrived nearly 8 weeks later on December 15.
I do agree with your premise that there is no hidden/secret full fat Polaris because every GPU release in the past has concentrated on promoting the higher end parts. Though AMD might be deliberately obfuscating I highly doubt it but it might just be a possibility.
Pretty much every single GPU release in the past few years has seen AMD one upped by Nvidia.
- 6970 was hyped, but a few weeks before release GTX580 drops in almost unannounced.
- 7970 was released with far too conservative clocks (925 when 1000+ was possible) This allowed GTX680 to exceed 7970 on release even though overall it was a worse spec'd GPU.
- 290X is eventually ready to beat Titan and GTX780, but a few weeks later Nvidia springs 780Ti to ruin AMDs party.
- R9 Fury X is hyped with HBM and as overclockers dream yet is beaten handilly by 980Ti in price/perf and VRAM. Not to mention overclocking.
Basically AMD's every move has been anticipated by Nvidia and maybe this time they have learned their lesson. Though I doubt it.
