All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad
is His slave and Messenger.
If the marriage contract was concluded in accordance with the madhhab of Abū Ḥanīfah
then it is a valid marriage, provided the remaining conditions – such as the presence of witnesses – were fulfilled. This is a matter of legitimate scholarly dispute (ijtihād), and the position of Abū Ḥanīfah
is a recognized and valid opinion; therefore, intercourse based on this contract is not considered zinā (fornication).
The mere fact that the spouses were aware of the ḥadīth does not in itself mean the approach they took was mistaken, provided they were laymen – for a layman is entitled to blindly follow (taqlīd) whomever he trusts. As for one who is a student of knowledge and to whom the greater strength of the majority's position, based on its evidences, became clear, then it is not valid for him to act contrary to what he holds to be the stronger opinion; in such a case, the marriage would be invalid due to the absence of a guardian (walī).
Renewing the contract as a precaution does not necessitate that it be preceded by a waiting period (ʿiddah) or a istibrāʼ (womb-clearing period); for even assuming the first contract was invalid, it is nonetheless of the type of contract that establishes lineage; lineage is therefore established in any case.
Allah Knows best.