As per Rule 5 of WBSR, pay means the amount drawn by a Government employee as the pay, other than special pay or pay granted in view of his personal qualifications, which has been sanctioned for a post held by him substantively.
As per existing order (No. 4730-F dated 25/05/99) of TA/DA, pay is defined as per the quoted rule of WBSR.
As per sub-rule (h) of Rule 3 of West Bengal Revision of Pay & Allowances '09, basic pay in the revised pay structure means the pay drawn in the prescribed pay band plus applicable grade pay but does not include any other type of pay.
So, this is really unfortunate as you said.
As per T.R. Form No. 23 (West Bengal Form No. 2446B) there is a provision of taking advance regarding TA/DA. But no provision for arear.
Then why an employee accept DA rate in pre-revised scale?