1.

Should Article 11(A)(3)(b) of the Sixth Council Directive 77/388/EEC of 17 May 1977 on the harmonisation of the laws of the Member States relating to turnover taxes – Common system of value added tax: uniform basis of assessment, (1) when it refers to ‘price discounts and rebates allowed to the customer and accounted for at the time of the supply’, be interpreted as meaning that the discount must also materialise at the time when it is granted, or can that discount materialise at a later point in time, as is the case where a retailer grants its customers discounts when they make a purchase that they can only use (deduct) on subsequent purchases, thereby reducing the price payable on those subsequent purchases?

2.

If the answer to the previous question is that the discounts ‘allowed to the customer’ referred to in Article 11(A)(3)(b) of the Sixth VAT Directive can materialise at a point in time later than the moment at which they were granted, must Article 11(C)(1) of the Sixth Directive be interpreted as meaning that the transaction in question falls within the scope of that provision and that VAT must be reduced in accordance with the formal requirement laid down by Portuguese domestic law in Article 71(5) of the VAT Code, including in relation to discounts granted on sales made to final consumers who are not taxable persons for VAT purposes?

3.

If the answer to the previous question is in the affirmative, must Article 11(C)(1) of the Sixth Directive be interpreted as permitting the Portuguese Tax and Customs Administration, in order to recognise the right to deduct VAT following the reduction of the taxable amount of a transaction falling within the scope of that article by the grant of a discount to final consumers (such as that at issue in the present case), to require that documents in the name of the customer showing the discount be issued as proof that the VAT was refunded (reducing the VAT previously overpaid), in view of the fact that Portuguese domestic law does not impose such a requirement for the documents attesting to the sale in connection with which the discount is granted and the sale on which the discount materialises, where the discount is shown on both documents, that is to say, at the time when it is granted and at the time when it is used, and the transactions are invoiced inclusive of VAT, in accordance with the special domestic law regime applicable to retailers?