Jennifer
There is an on-going discussion on RightsNet about this issue, you'll see that it pre-dates the DWP announcement by several years! So much for it being a recently discovered issue.
www.rightsnet.org.uk/forums/viewthread/5928/ If you look at the last couple of pages the issue of payments being limited to 2014 has been raised and is generally agreed to be incorrect, however, as of today, no one appears to have articulated why it's incorrect in a format that is arguable with the DWP.
I'm afraid it's a case of watch that space at the moment.
Gordon