You can get premiums backdated to when your DLA is awarded from on appeal if the only reason you didn't get it in the first place was because you hadn't been awarded the DLA.
So if you were entitled to ESA/IS on incapacity grounds and your income and capital were such that you could get it, but you didn't get premiums because you didn't get DLA, then when you win your appeal, you can get your premiums paid from the date that the tribunal says your DLA should be paid from (i.e. the date of the original decision).