An invoice should include the following: the date of issuing, the date of executing or finalising the delivery of goods, when you performed the service and the date of receiving money, as mentioned in Article 108b, Section 1, Subsection 4 of the VAT Tax (Dz. U. of 2011, No. 177, Item 1054, as amended), if the date is specified and is different than the date of issuing the invoice.
According to the general rule expressed in Article 19a, section 1 of the VAT Act, the tax obligation arises the moment the goods are delivered or the services are provided. Thus, the tax becomes due and payable in the month of the delivery of goods or provision of the service and, as a rule, it should be accounted for within this settlement period.
In accordance with Article 7, Section 1 of the Act, the delivery of goods means the day of transferring the right to manage the goods as the owner. The delivery of goods usually means a physical release of such goods to the taxpayer or a person authorised to collect the goods on behalf of the taxpayer.
Currently, taxpayers are allowed to issue invoices even 30 days before the goods are delivered. In such case the seller does not always know when the rights to manage the goods as the owner, meaning when the delivery of goods will be transferred. Those invoices, as a rule, do not have to specify the date of delivery, unless the date in known to the seller on the day of issuing the invoice.
Source: Gazeta Podatkowa