To unravel the mystery in post #36 of this thread:
When the quattro GmbH launched the sedan in 2009 every C6-coded Audi went through a facelift. The A6 models got headlights with an LED-string, larger sidemirrors with integrated LED indicators, all sedans got wider taillights with higher reaching rearbumpers...
The C6 RS 6 Avant was already on the market since 2008 and already equipped with the new mirrors and custom-headlights. So the only visual change at the exterior were white reflector indicators in the Avant-taillights. Because the RS 6 uses the same taillights as the lower spec A/S6 range they only had to install the reworked ones to sell the 2009+ RS 6 Avants as relaunched models