Could there be real Christianity in an illiterate small tribal society, for example hunter-gatherers; in which all knowledge is orally transmitted?
This is something of a litmus test for me, because I feel that the answer must be yes - assuming that God is creator and our Father who wants all his children to have the chance of salvation.
But if the answer is yes; then much of what traditional Christianity assumes to be essential is revealed as inessential - for example The Bible, Priests and Sacraments. Also Orthodoxy - in the sense that precise transmission and testing of belief is not really possible; 'heresies' of many types would presumably be endemic.
Furthermore, it seems to me that in practice Christianity, under such conditions, needs to be a matter of direct personal revelation, on something approaching (not reaching) a universal basis - that almost-everybody would need to be able to know Jesus Christ and his work and gifts - personally, directly, frequently, and with sufficient validity and precision to choose salvation.
Anyway - this is a 'thought experiment' that often comes to mind; perhaps because the corruption of the church, the Bible, and everything else begins to converge modern society onto something like this situation.