(Adapted from my reply to a comment from 'Bookslinger'.)
There is all the difference in the world according to whether I know something for myself or have merely read about it with assent. I don't know it until I have thought-it-through.
I think it is the same for nearly everybody. Things that are implied merely, or stated merely, do not have life, do not have influence.
The implications of a fact... that is what is hard to know. That is the difference between scholarship and holiness.
At any rate, I have certain 'issues' that are important for me, and I have never seen the fact that we used to know Jesus given as an explanation for why everybody therefore knows Jesus without being told about him. For example, why the plan of salvation worked and works and will work without any church (and despite some/ most churches).
Because, taken seriously - the fact that each person knew Jesus means that learning the history of Jesus is not necessary - nor is the accuracy of the history we are told. Knowledge of scripture is not necessary; nor is the existence of scripture - we do not need the Bible.
All of which is very important in a world where (and increasingly) history is anti-Christian by assumption, where scripture is being deliberately mistranslated, and where scriptural teaching is mostly false and inverted.
I have, from at least age 4, had a spontaneous aversion to the fact that Jesus was born at a time and place that was not my own - I don't like the Middle East setting.
I am deeply troubled about insisting on the absolute (verse by verse) accuracy of the Bible (especially when ignoring the specifics of translation) when I can see for myself new 'translations' being systematically distorted and inverted in front of my eyes (eg. in the 'gender neutral' versions officially used in the Church of England).
I need to known Jesus directly.
Yes Jesus is alive here and now, but that is not sufficient when 'everything' really does hinge upon the truth of historical facts, including that Jesus did something at a particular time and in a particular place.
(Note: I nowadays regard the philosophical - Platonically-derived - stuff about God being 'outside time' as self delusion/ rationalisation. So, I believe that really Jesus did do what he did at a particular point in history; with a before and an after.)
That we knew Jesus premortally means that we each already know the plan of salvation by which Jesus would enable Men to become gods (resurrected immortals). We therefore know the historicity of his incarnation and its purpose.
We don't know the specific details (dates) of his life and death from this source - because these were not pre-ordained, and depended on agency. But we do know Jesus's nature, why he was chosen, what it was all for; and therefore we know enough to decide to love, trust and follow him...
Each and every one of us already knows enough. What is needed (as usual) is to become aware of what we already-know...