All of the hundreds of different Christian denominatios use verses from the Bible to support their often-contradictory beliefs. Thus the Bible or any other source of information about God's truths (ie: Dead Sea Scrolls, Nag Hammadi Library, etc.) can be used to support true as well as false doctrines. So is biblical support sufficient to be sure that our beliefs are true and accurate?
Remember, our Saviour said, "And this is life eternal, that they might know thee the only true God, and Jesus Christ, whom thou hast sent." John 17:3, giving us an understanding of the importance of gaining an accurate knowledge about Him and His father. Indeed, He said our eternal life depends on such knowledge. Would He then leave us to our own understanding of the Bible or any other book, alone, to arrive at the truth?
No! He has given us a more-sure source, if we will only learn to use it. He said, speaking of the Holy Spirit, "Howbeit when he, the Spirit of truth, is come, he will guide you into all truth: for he shall not speak of himself; but whatsoever he shall hear, that shall he speak: and he will shew you things to come." John 16:13 So whether the sources for our beliefs are correct, or not, really depends not just upon 'biblical support', but even more on whether we are allowing ourselves to be guided by the Spirit of Truth.
In conclusion then, our Saviour's promise of sending the Spirit of Truth might be considered one type of 'Biblical support' for our opportunity and ability to discover truths in support of our developing beliefs in non-biblical sources.