Jianne
Award lengths are based on the possibility of the claimant's conditions changing, this doesn't just mean improving it also covers a deterioration!
The award length is part of the Decision and can, therefore, be challenged at MR or appeal but will need to provide convincing evidence that a longer award is justified, this is primarily a medical decision and the DM has no medical training.
Gordon
Nothing on this board constitutes legal advice - always consult a professional about specific problems