Scarborough,
My section A form had a new number on it too, I spoke to my lawyer who sent a case-specific enquiry, apparently the VO had probably made a clerical error. Make sure you give your DMP a few previous documents that indicate your correct file number BXXXXXXXXX and have them include it when they send in your medical results. Your DMP will either cross out the wrong file number and indicate the correct one or enclose a letter explaining the two file numbers. My understanding is that once you are given a file number, it typically stays the same.
All the best,
SF2005