Prior to the mid-20th century, there was no such thing as Reformed Baptists. From the 1630s until maybe the 1950s, they were largely known as Particular Baptists and quite distinct from the Reformed camp (having separated over infant baptism, c. 1638). That term "particular" is what set them apart as Calvinist, insofar as they affirmed a particular (i.e., limited) atonement. So, their soteriology is Calvinist but their theology is not Reformed (and their covenant theology was and is... well, weird).
Thus, we have Reformed theology (which is more than just Calvinist) and Particular Baptist theology (which is Calvinist but not Reformed). Their adoption of the term Reformed Baptist has led to needless confusion, especially their dispensationalist wing.
Covenant theology was developed from the 15th century onward by Zwingli, Calvin, Bullinger, Olevianus, Witsius, etc. However, although it was popular, it was certainly not the consensus; let's not forget the Anglican and Lutheran churches of that period. I don't think Lutherans even have a covenantal view of salvation. It has a more promissory focus, emphasizing grace through faith alone and a distinction between law and gospel. If Reformed theology is covenantal, then Lutheran theology is sacramental (but not sacerdotal). As for the Anglicans, the Thirty-Nine Articles do not contain a developed covenant theology but they implicitly reflect covenantal ideas, and the Book of Common Prayer uses covenantal language in its liturgy, particularly in the baptismal service.
Edit: John Nelson Darby began systematizing dispensational ideas circa the 1830s, so 200 years after the development of covenant theology.