Manufacturers seem to be manipulating the temp ratings, loft and fill ratings on sleeping bags.
Mine shows 850 down fill, but current version of same model show 800 down fill. Probably cheaper to fill the bag with less expensive fill to a higher loft than to access/purchase a dependable source of the most premium down fills. Even their "-40F rated" bag is filling with 800 down, but to a much higher loft AND weight. Manufacturers use the term "sustainability" prominently for urban snowflake sensibilities. Couple of years ago they were offering "900 down" for their expedition bags.
My "rating" on bag indicates -33.3F (Extreme), 6 deg F (Lower Limit) and 18.8F (Female - Comfort)...have used it in comfort at a measured -10F in a single wall alpine tent and ThermoRest All Season air mattress with fitted mattress sheet. The ORIGINAL advertising gave my two year old bag a "-20F" rating. Newest version states "...for mountaineers and backpackers encountering conditions down to 0 deg Fahrenheit."
Use your best judgement...
