Switch Date

Key Switch Date in Fx Vol Spec refers to an optional date Tˢʷⁱᵗᶜʰ - that defines when the long term definitions specified in LT ATM Def and LT Delta Def are valid.

More precisely, the ATM (At-The-Money), RR (Risk-Reversal) and BF (ButterFly) options, the vol quotes of which are specified in the table supplied through the key Vol Set, will have their ATM and Delta defined according to the long term definitions if their expiry T satisfies T >= Tˢʷⁱᵗᶜʰ

If the entry here is left blank, the Tˢʷⁱᵗᶜʰ is defined by a potential entry in Switch Tenor
If the latter is missing, the Tˢʷⁱᵗᶜʰ is set to infinity, which means the LT ATM Def and LT Delta Def entries are ignored.
If the entry here is provided, the Switch Tenor entry must be left blank.