1.

Does Article 72(1)(e) of Directive 2014/24, (1) in conjunction with Article 72(4)(a) and (b) thereof, permit a national rule, or practice of interpreting and applying that rule, according to which a breach of the rules on substantial modifications of public contracts can be invoked only where the parties have signed a written agreement/annex amending the contract?

2.

If the first question is answered in the negative, does Article 72(1)(e) of Directive 2014/24, in conjunction with Article 72(4)(a) and (b) thereof, permit a national rule, or practice of interpreting and applying that rule, according to which an unlawful modification of public contracts may take place not only by means of a written agreement signed by the parties but also by joint acts of the parties which are contrary to the rules on the modification of contracts, and are expressed in communications and the associated paper trail (such as that in the main proceedings), from which a common intention regarding that modification can be inferred?

3.

Does Article 72(1)(e) of Directive 2014/24, in conjunction with Article 72(4)(a) and (b) thereof, permit a national rule, or practice of interpreting and applying that rule, according to which, in a case such as that in the main proceedings (where a maximum time frame and the deadline for performance of the contract were specified in the contract documents; the time frame also serves as an indicator in the methodology for evaluating tenders; performance of the contract actually exceeded the maximum time frame and the deadline laid down in the documents, without there being any unforeseeable circumstances, and the contracting authority accepted the performance without any complaints and did not seek to enforce a penalty for delay), performance of the contract in a manner contrary to the conditions in the part of the contract and contract documents which relates to the time frame, without there being any unforeseeable circumstances or complaints on the part of the contracting authority, is to be interpreted only as a form of improper performance of the contract and not as an unlawful substantial modification of the contract concerning the part relating to the time frame for performance?