Key _Synthesized Curve in refers to the curve synthesized using the data supplied in
This is the curve built internally in order to produce the final implied curve.
As such, it implies the exact same discount factors as the final implied curve.
Note this key is prefixed by _, which indicates it is regarded as a read-only part of the object's data and therefore its associated value cannot be edited.
For that reason it does not appear as part of the input data.
It carries informational only value for the user and appears as part of its contents.
Also it completely depends on the remaining object contents and therefore is never part of the exported object's data.