The invoice date can be the same as the purchase date. Consumers can issue VAT invoices within 7 days with promissory notes and ordinary invoices within the same month. After the above period, they can't issue invoices. After the invoice is issued, it can always be used as a voucher, and there is no time limit for ordinary invoices. The invoice has not expired. Only when the tax authorities stipulate that the invoice cannot be used and a new invoice is needed can it be considered overdue. It is not stipulated that the invoice can still be used. The special VAT invoice only says that it must be certified within 90 days after the invoice date, otherwise it cannot be deducted.