Key As Of of function Price in Tradable refers to an optional date T₀ that sets the valuation (or trade) date, which is the date associated with the pricing output.
If not specified, it is regarded equal to the currently set global valuation date Tᴳ₀
All cash flows are discounted down to that date T₀
If T₀ differs from Tᴳ₀, all other input data will be reconstructed - if permitted - using T₀ as reference.
For example, an input object of type Yield Curve would be rebuilt using T₀ as its effective trade date, but only if its own Key Market::Trade Date setting allows for this substitution by not having been previously set to some specific fixed date.
This means, the valuation would proceed using curves that - when observed at T₀ - are (almost) identical in shape to the corresponding spot curves observed at Tᴳ₀ and not to their corresponding T₀-forward curves observed at Tᴳ₀
It follows that if T₀ > Tᴳ₀, the produced price will NOT equal the T₀-forward price obsrved at Tᴳ₀
If T₀ is set to the date of the last relevant cash flow, the evaluation outcome will be zero, except if the flag Trade Date CFs is set to true.