If I haven't misunderstood "Signature date" is set at the time of mandate is created. With the same date of "Creation date". Why?
I think it could be empty and It would have to be able to be defined a posteriori.
I see this commit d98f628. Maybe DtOfSgntr could be defined with "Signature date" if is defined and with "Creation date" if "Signature date" is empty?