@Scott-C if the email address isn't connected to your VM account, then it is regarded as orphaned and as such is liable to be deleted along with all the email within it at any time.
So if you are a current VM broadband customer, have you always been a customer (or a customer of one of the precursor companies) or has there been a break in service at some point in the past? Have you moved house since the addresses were set up?
Any of these could have caused the addresses to have become orphaned. Now if you are a current subscriber, then there is a chance that the addresses could be linked retrospectively to your BB account - but its isn't guaranteed.