Voucher number and reference number

Can i make voucher number and reference number same for all my old sales entries?

please explain clearly.
for bank or cash transactions, there is no separate fields for voucher and reference numbers.

Just now i have started using tally for my industry…I have finished entering all my sales invoice details. But starting from july month entry my voucher number and reference number are not same in sales register. The voucher number is my invoice number in the bill supplied to our customers. But reference number is one number ahead of it(it comes as against new ref.no). So when i see bills payable it shows the reference number which is not same as invoice number. This creates confusion in knowing the invoice number.
Just now i have started using tally entering all the old month data. Kindly help

you keep saying you are using Tally.
this forum is for discussions regarding the use of Manager accounting software and not Tally.