Does anybody know for sure that the "mature stocks" are actually S-W wheated bourbon?
Depends on what you want to define as S-W wheated bourbon. The stocks I have seen in the past were "Old Fitzgerald", from both DSP 16 and DSP 113. At that time is was being blended into Crown as Chuck stated above. About 5 years ago early conversations with a Diageo Exec were promising regarding getting some of these old stocks released for others to barrel as single barrels. Didn't go anywhere at the time but as we know now, other bottlers have gotten access to some of this stock.
No US taxpayer was harmed in the making of my Ford racecar.