Jews for the past few thousand years were demonstrable masters at preserving the Old Testament texts.1 This is relevant because it was Jews who also preserved these texts for the remaining years that we don't have manuscript confirmation of. We can rationally expect the trend to hold.
• Gleason Archer: “[even though it is] a thousand years earlier than the oldest dated manuscript previously known (A.D. 980), [the Isaiah copies] proved to be word for word identical with our standard Hebrew Bible in more than 95 percent of the text. The 5 percent of variation consisted chiefly of obvious slips of the pen and variations in spelling.” • Norman Geisler and William Nix: “Of the 166 words in Isaiah 53, there are only 17 letters in question. Ten of these letters are simply a matter of spelling, which does not affect the sense. Four more letters are minor stylistic changes, such as conjunctions. The remaining three letters comprise the word 'light' which is added in verse 11, and does not affect the meaning greatly. Furthermore, this word is supported by LXX and IQ Is. Thus, in one chapter of 166 words, there is only one word (3 letters) in question after a thousand years of transmission--and this word does not significantly change the meaning of the passage”[General Introduction to the Bible (Moody Publishers, 1986), 263.]
• Second, various accuracies of the Old Testament are best explained as being remnants of carefully preserved historical accounts. For example, scribes for thousands of years accurately perserved and transliterated 184 verified names of kings etc. • Robert D. Wilson: “In 144 cases of transliteration from Egyptian, Assyrian, Babylonian and Moabite into Hebrew and 40 cases of the opposite, or 184 in all, the evidence shows that for 2300 to 3900 years the text of the proper names in the Hebrew bible has been transmitted with the most minute accuracy. That the original scribes should have written them with such close conformity to correct philological principles is a wonderful proof of their thorough care and scholarship; further, that the Hebrew text should have been transmitted by copyists through so many centuries is a phenomenon unequaled in the history of literature” … “Thus analogical evidence as well as the evidence of the documents forces us to the conclusion that the spelling of the proper names of the kings must go back to original sources; and if the original sources were in the hands of the composers of the documents, the probability is that since the composers are correct also in the sayings and deeds which they record concerning these kings.” [A Scientific Investigation of the Old Testament, 1959.] In saying Jews were masters at preserving their holy texts, we are not saying they are perfect (even for Isaiah, we only see a 95% correspondance). However, there is more than enough to justify belief in any given doctrine, and if need be we can do textual criticism on any particular text to see how well substantiated it is in particular.
We have no manuscripts dating to a time close enough for us to trust.
In response, however, we have several early manuscripts. The New Testament was written approximately AD 50-90, and yet we have:
P52 - AD 125 (or AD 100)
P90 - Second century (John)
P66 - Second century (John)
P98 - Second century (Revelation)
P46 - c. AD 200-225 Pauline epistles
P4, P64, P67 - Second century (Luke & Matthew)
And so what if we didn't? We have enough early church citations to reconstruct the whole New Testament.1
NT manuscripts disagree around 300,000 times1
But so what?
Wallace (summing up the differences):