RG1 register-opening quantity is mismatching with actual quantity

Dear Experts,

My client has implemented SAP in 2009 and never used excise registers for long time. 2012 mid started giving training to users and finally they fixed a cutover date on Jan 2013,

upload Chapter material combination with material status as RG1

Uploaded opening quantity in J_1irg1bal table as on 01.01.2013

started update,extract and print

but we have encountered some red traff issue is due to the cumulative receipts are not tallying with cumulative issue.we have rectified the issue and took 2 months time. now the client is telling the actual opening quantity and system opening quantity are not same

so how do i justify whether the quantity is showing in the system is corect or not or what can i do to solve this issue please through some light on it?

With regards,

Pratheep