CAC = choice, high-end, and possibly under-graded. Other services would likely call XF45.Even PCGS might at some point. Just 125 survive as per PCGS Coin Facts. Many tallied in the population reports (including CAC's) are resubmissions or crossovers of the same coins.
Low 21,100 mintage, few saved. The item "1856-O PCGS XF40 CAC 125 Survive per CU $1,800 APR Sleeper $2.50 Quarter Eagle" is in sale since Friday, August 14, 2020. This item is in the category "Coins & Paper Money\Coins\ US\Gold (Pre-1933)\$2.50, Quarter Eagle".The seller is "certifiedcitynet" and is located in Philadelphia, Pennsylvania. This item can be shipped to United States.