I think it was good that the British Embassy phone your Fiancee, first before issuing the visa, like what they said that "if it's dated from now it wouldnt leave enough time after the wedding to apply for FLR before the fiancee visa expired. "
So I would take it as a advantage, because at least you are given the chance to give your explanation.
I think its best you immediately get in touch with the B. Embassy and explain to them that originally your Fiancee wrote 30 March 09 and it was the VFS Staff who told her to change it.
Congratulation, as I am hundred percent sure that your application is successful.
