The Catechism of the Catholic Church says (#105), "God is the author of Sacred Scripture." Further, (#106)
[The human authors of scripture]consigned to writing whatever he wanted written and no
Therefore, there is no part of the scriptures that is merely human and potentially erroneous. God is Truth, and can neither deceive nor be deceived. Thus, I believe that the answer to your question is that all of Genesis is to be considered historical, unless there is a reason to believe that the literal sense is different (as has been suggested with Genesis 1).
If you look at Pius XII's Divino Afflante Spiritu, you will find this spelled out:
having been written under the inspiration of the Holy Spirit, they have God for their author, and as such were handed down to the Church herself." When, subsequently, some Catholic writers, in spite of this solemn definition of Catholic doctrine, by which such divine authority is claimed for the "entire books with all their parts" as to secure freedom from any error whatsoever, ventured to restrict the truth of Sacred Scripture solely to matters of faith and morals, and to regard other matters, whether in the domain of physical science or history, as "obiter dicta" and - as they contended - in no wise connected with faith, Our Predecessor of immortal memory, Leo XIII in the Encyclical Letter Providentissimus Deus, published on November 18 in the year 1893, justly and rightly condemned these errors and safe-guarded the studies of the Divine Books by most wise precepts and rules.
The first and greatest care of Leo XIII was to set forth the teaching on the truth of the Sacred Books and to defend it from attack. Hence with grave words did he proclaim that there is no error whatsoever if the sacred writer, speaking of things of the physical order "went by what sensibly appeared" as the Angelic Doctor says, speaking either "in figurative language, or in terms which were commonly used at the time, and which in many instances are in daily use at this day, even among the most eminent men of science." For "the sacred writers, or to speak more accurately - the words are St. Augustine's -  the Holy Spirit, Who spoke by them, did not intend to teach men these things - that is the essential nature of the things of the universe - things in no way profitable to salvation"; which principle "will apply to cognate sciences, and especially to history,"
Finally it is absolutely wrong and forbidden "either to narrow inspiration to certain passages of Holy Scripture, or to admit that the sacred writer has erred," since divine inspiration "not only is essentially incompatible with error but excludes and rejects it as absolutely and necessarily as it is impossible that God Himself, the supreme Truth, can utter that which is not true. This is the ancient and constant faith of the Church."
From these considerations, I would say that "for the sake of salvation" from Dei Verbum in this quote should be interpreted as the motivation for God's revelation in the scriptures and not as a restriction of inerrancy to moral and theological subjects.
Therefore, since everything asserted by the inspired authors or sacred writers must be held to be asserted by the Holy Spirit, it follows that the books of Scripture must be acknowledged as teaching solidly, faithfully and without error that truth which God wanted put into sacred writings (5) for the sake of salvation.
In the area historical accuracy, the Old Testament has been proven a very reliable witness to the ancient, ancient world. One should be careful about finding historical inaccuracies there, because the authors of the Old Testament, even at the latest date argued for the time of writing, were far closer to the events and society of the times they depict than we are.
A little anachronism is to be expected in human language. For instance, we often talk about things happening in Israel or Turkey when it is only a geographical accident that they are included in the current borders of the political entities that bear those names today. That doesn't make the statements any less true.