Article 26 does not prohibit issuing invoice in advance or mandate that invoice should be annually issued. It merely states that the date of supply gets triggered at the earliest of issuance of tax invoice or receipt of payment, date of payment as per tax invoice or receipt of payment. So one may issue tax invoice of PDC due dates or at the end of 12 months as well.

The date of supply of Goods or Services for any contract that includes periodic payments or consecutive invoices shall be the earliest of as mentioned by you But provided that it does not exceed one year from the date of the provision of such Goods and Services. what is meaning of this part -what does not exceed one year from date of provision of such goods and services?

It means where provision of goods/services have been completed then the invoicing cannot be delayed beyond 12 months citing earlier of issuance of invoice or receipt of payment. For example, in the given case, if the invoicing was done on quarterly basis based on receipt of payment and if there is a payment delay in one quarter, the supplier is not obligated to account for the VAT on the same until the payment is received, provided, the delay does not go beyond 12 months. At the expiry of 12 months (from date of payment is due as per tax invoice which would have been the payment date as per contract) VAT will have to be accounted for by issuing invoice regardless of whether payment was received or not.