How do we know that? We have to have some sort of legitimate biblical study to determine what is corrupt. Certainly, the guidance of the Spirit is critical, but plenty of people claim all sorts of things were inspired by the Spirit. A few years ago, I received a letter from someone claiming that God had revealed to him the corrected text of Scripture and anyone could come and view their choice of passage on a particular afternoon. My interpretation will be biased in light of my background, preferences, etc. My job is teaching, keeping the department running, dealing with all sorts of paperwork and requests, and getting in a little research. Other people have had much more opportunity to study the Bible in depth. They also, though not perfect, will have different biases and so are likely to recognize some of my errors. Remember the many verses about seeking counsel, heeding the teaching of the elders and apostles, etc.
Thus, our responsibility is to seek out sound teaching, to find what those who have more experience have to say, to improve our understanding and correct the corruptions. Checking the teaching from much earlier scholars, as you suggest, is an excellent approach - living in a different culture, they have quite different biases and often see through what we are blind to. Also, anything that has stood the test of time is worth looking at, whereas much popular at the moment will vanish like surplus copies of “88 reasons why Jesus will return in 1988”.
But it is also necessary to have due diligence in checking what people taught through history. The claim that the church held a young-earth position until modern science came along is an “Enlightenment” lie, aimed at making Christianity look stupid, for example. There’s plenty of corrupt claims about history to beware of, also.
The fact that the Old Testament and New Testament fit so well is an important reason against accepting creation science claims. Both teach primarily what we are to believe concerning God and what duties He requires of us. We should not separate out Genesis 1 and claim that it is talking about scientific history rather than theology. Creation science in general, and flood geology in particular, is an extreme of dispensationalism, having God working in wildly different ways in the past (indeed, simultaneously doing multiple incompatible actions) rather than consistency in God’s working from beginning to end.
Indeed, religion is about God, but there’s no reason to take seriously someone’s claims about God that are based only on whatever they want God to be like. Good scholarship about God teaches us to better understand our religion.
Just because someone has a big name PhD does not mean that their scholarship is theologically sound. Nor does my PhD studying fossil and modern mollusks mean that I am an authority on unrelated topics. I am not saying that we should just defer to anyone with more letters after their name. Rather, like the Bereans, we should study Scripture ourselves to assess claims as well as we can, and listen to those authorities who do show credible evidence of faithfully investigating Scripture, throughout church history.