When you set up a new Supplier (Creditor) in QuickBooks, there is the facility to add an opening balance to the supplier record, as at a date that can be selected from the calendar.
By entering a figure on the supplier record, what QuickBooks is doing behind the scenes, is generating a bill. This bill can somewhat be edited, the name, the date, the amount etc but a tax code cannot be added to the tax column.
If the business is registered for GST on an accruals basis, this is fine because the GST would have been picked up in the previous accounting system. However, if the business is registered for GST on a cash basis, then once this bill is paid, the GST should be reported – and the GST figure is not split from the total expense.
Another point to consider is that the opening balance may be made up of more than one outstanding bill and may cause havoc if you are paying per invoice, reducing the one opening balance amount, but having no concept of aging of the creditor, or individual bill totals. Instead of using the opening balance feature on the supplier record, redo any outstanding bills in the new data file as at the date that it was originally generated. If the business is registered on a cash basis, add the appropriate tax code to the tax column. There is no need to add the tax code if the business is registered for GST on an accruals basis.
There would still be original documentation, so not much detail is required when the bill is re-entered. This would then give accurate aging reports as well as report the GST on purchases correctly.