I think this may be more suited to /r/asktheology, since the point is debatable among the different denimonations. I know at least Catechism of the Catholic Church explicitly states the opposite.

122: The Old Testament is an indispensable part of Sacred Scripture. Its books are divinely inspired and retain a permanent value, 92 for the Old Covenant has never been revoked.

If you're interested in why or how, I suggest starting with Marcionism, the movement in the early church to seperate the still new christian faith from the Jewish tradition.

Firstly, be cautious with /r/AcademicBiblical. It's common to hear things stated as fact with little evidence behind them, and views at one end of a spectrum of opinion stated as academic consensus. Still worth asking there, but just apply a bit of a filter. They are good on languages, though. Also don't expect them to be /r/AcademicChristian!

In respect of your question: the NT doesn't present a single view on whether there is a new covenant. Matthew presents the most traditionally Jewish view, showing Jesus as requiring full obedience to the law, with "righteousness surpassing the Pharisees". There doesn't seem to be any sense of a new covenant replacing the old. I think you're taking "fullfilment" (used in each of your three quotations) to imply "replacement" or "abolition": that doesn't seem to be clearly implied by the text, and in the case of Matthew 5:17 it seems contraindicated.

We know from the writings of Paul that there was a tension between the Pauline and Judaising Christians (see Galatians, for instance), so using your preferred terminology, it seems that there were early Christians who did not believe that the OT covenant was abolished. This tension continued for about 150 years. For instance, a notable group on the more extreme end of the Judaising side was the Ebionites. This group used a Hebrew gospel said to have been written by the apostle Matthew, of which we only have a few fragments now. Whether that gospel has any relationship to the Gk gospel we call Matthew we don't know - currently the weight of academic opinion is against it.

My reason for mentioning this is that it casts doubt on whether your question is answerable in historical rather than theological terms. Even in the earliest stages (Galatians was written about 27 years after the crucifixion, and before the earliest gospels that we now have), there was argument as to whether the OT covenant was abolished. It seems unlikely that we will be able to reconstruct what Jesus said on the subject.