A couple of things. First, clearly each of those people believed in Jesus. That is why they were saved. But, note, that was before his death and resurrection and before God provided the New Testament.
Paul makes it clear that there is a specific Gospel that must be understood and that it can only be understood if it is preached. Thus the call to evangelism in the Great Commission.
There are many people who have heard of Jesus but that does not mean they have believed in their heart and confessed with their mouth. My fear is too little understanding rather than too much.
I don't believe that a correct understanding of doctrine is a check list. It isn't equivalent to legalism (saved by what we do rather than what we believe).
But Jesus makes it clear that it is belief that saves, even now. (see, e.g., John 3, Mark 16).
Paul makes it clear that there is a specific Gospel that must be understood and that it can only be understood if it is preached. Thus the call to evangelism in the Great Commission.
Knowing and understanding the Gospel is good and necessary. Teaching people about the Gospel helps people to know about Jesus, and therefore believe in Him. But many people who do not believe, nevertheless know and understand the Gospels -- just knowing and understanding does not confer salvation. Only belief does that.
don't believe that a correct understanding of doctrine is a check list. It isn't equivalent to legalism (saved by what we do rather than what we believe).
But it's not necessary for salvation, either.