The way I see it, is that the 1939 register has been contaminated by its subsequent use by the NHS.
Both my mother and father died in Hospital prior to 1991, one would expect that the NHS would have recorded them as having been deceased.
There seems to be an "element" or a hint of mis-selling in what is being advertised about the 1939 "register"
FindMyPast were told people who had died before 1991 were marked on the register with a "D", that is what they use to determine whether people born after 1915 are alive or deceased.
As we have been told (a copy of their mailing from Genbrit was posted on a Rootschat forum) by someone who worked on the register during their working life some (many ?) doctors did not inform the NHS when their patients died as that would mean them losing funding.
If that is added to the number of clerical errors that would occur in and large database such as this it is easy to see how a large proportion of deceased people would not be so marked.
FindMyPast have a team who are attempting to reconcile people whose deaths are recorded in the deaths register with those on the 1939 National Registration but this in itself is a huge task.
As many family historians know it is not always an easy matter to prove a death on the register corresponds to a birth on the birth register.
We as family historians can help others by sending in digital copies of death certificates we have for relations known to be on the '39 register, this will not only help FindMyPast it will help TNA and also future licencees of the '39 register. More importantly help other family historians and local historians in the future.
Cheers
Guy