Michael,
This is a point of some confusion. The Brix scale used to measure (for example) grapes in winemaking provides a percentage of fermentable sugars. 23 would mean that 23% of the puree by weight is fermentable, corresponding to what you would get if you stuck a hydrometer in the puree and read off the brix scale.
However, potential in a grain record is the yield potential of the dry grain by weight, which is not directly convertable to SG. For example a 100% yield grain (i.e. sugar) would have a max potential of 1.046, which means that 100% of the weight is converted to sugar in solution. In the case of the puree, a lot of it is water and not converted directly to sugar. This is why BeerSmith limits this yield to 100%.
To get the correct yield of your puree, you need to enter the 23 as the yield (23% of it is fermentable), which provides a yield potential of 1.011
Cheers!
Brad