time-limited appeal and powers of a tribunal

I have a client who has an ongoing DLA appeal regarding a decision refusing any entitlement.  The decision was made over a year ago.  Following a change of circs, he recently submitted a new claim and was awarded low-rate care, high-rate mobility.  The appeal has now been limited to 26/05/2011 and is for a period of about 15 months.  I have advised the client that I do not think he will succeed as I do not think he qualified back then.  The client has decided to continue with the appeal on his own, but I would like to advise him of all possibilities.

What powers will the tribunal have regarding his new DLA award?  Do they have to ignore this new award completely, or if they see fit can they raise doubts about my client’s current award and refer this back to DWP to review entitlement?