ESA process started pre March 2011 changes

Im scatching my head about this - I have just been asked to assist a client lodge an ESA appeal. She was issed the ESA50 Form at the end of March 2011 just before the new descriptors came into use and returned it just after the new descriptors came in, her medical examination took place last month.  The DWP have made their decision using the pre March 2011 descriptors…. Have they made a mistake or is it the case that because the ESA50 was sent out just before the pre March 2011 changes she is being tested under the old descriptors?

No mistake and Yes

It is the date of the medical which is the key.  The position is roughly this.  All medicals prior to 28/3/11 use the old descriptors.  All medicals between 28/3/11 – 28/9/11 can use either the old or the new.  The ESA50 will determine which.  All medicals after 28/9 11 will use the new descriptors.

Thanks for your posts.  Her medical was on the 14/09 so from your responses she was therefore assessed under the old descriptors as her ESA50 was sent pre March 2011.