I’m seeing quite a few examples of invoices still being issued at the old 12.5% GST rate. In one case the supplier said they used the old rate because the goods were delivered in September.
Invoices issued in October at 12.5% are probably incorrect. Sometimes they will be okay but as a general rule they will be wrong. This is important if the purchaser is a business because they should be able to claim GST at the 15% rate on the expense but must have a valid tax invoice to do that.
Also, some businesses are having trouble with automated systems and credit notes for pre 1 October sales are being issued at 15% when they should be 12.5% .
During this transitional period it will pay to check invoices and credit notes carefully.