Key Trade Date in refers to an optional Date value that represents - when set - the fixed date when the respective market quotes have been observed in the market.
If not explicitly set, no such fixed date is associated with this object, which is regarded as having a "dynamic" trade date, meaning that the respective quotes are regarded as being observed at the currently applicable global trade date, which may be context-dependent.
An error is issued if a fixed trade date is used in a pricing operation with a different global trade date.
It is generally more flexible to use Market objects with dynamic trade date, i.e. with no date being set here.
A useful function that returns information on whether a Market object has dynamic trade date or not, is the