Whether it is possible to retroactively issue Purchase Confirmations to secure indirect export performance

I am in a situation where I need indirect export performance data dating back to last July to receive financial benefits. I am wondering if it is possible to retroactively issue Purchase Confirmations. If an exporter requests it, can Purchase Confirmations be issued retroactively from last July? Without modifying the tax invoices to convert them to zero-rated tax, can I receive a Purchase Confirmation based on the currently issued tax invoices and subsequently obtain proof of indirect export?