Hi WW. I think we can say that no, VPW did not cite his sources in a consistent, professional or scholarly way that would allow a reader of most of his work to track it.
I used those three words deliberately - there are some references here and there but there is a notable absence of him foot noting sections of what he published under his name that were clearly and closely identical to other work of other writers and doing it consistently or in such a way that it would be on record. Nor did he observe professional and legal best practices in that area, nor educational standards.
He did talk about them, at times. He referenced Bullinger, Leonard, etc. etc. but never in a way that credited them, nearly always making note that they had all somehow stepped into error at some point or stopped "believing" God at His Word.
I think one of the likeliest reasons he did that was to support his claim that God would teach him like no other since etc. if he would teach that to others. If he referenced huge chunks of his ideas and language used to express them to others having it first it would erode that claim.
The best thing he could have done was invite all critics including those he quoted, to question and negate his work if they so desired and then let the pieces fly as they might. That would have suited his two-fisted mans-man motorcycle riding personae he promoted. Instead he talked about it in ways that allowed him to "credit" them while making sure the listener understood they were not fit to judge his ultimate use of their words. Matthew 5 – "Again you have heard that it was said to those of old, 'You shall not swear falsely, but shall perform your oaths to the Lord.' But I say to you, do not swear at all; neither by heaven, for it is God's throne nor by the earth, for it is His footstool; nor by Jerusalem, for it is the city of the great King. Nor shall you swear by your head, because you cannot make one hair white or black. But let your 'Yes' be 'Yes' and your 'No,' 'No.' For whatever is more than these is from the evil one."
"Honesty" is a moving target for a lot of people. In the Way it's reserved for "the truth of God's Word". Everything else to them is a "fact", unreliable and invalid. Facts are ignored and replaced by "what's the Word say?"....and of course the Word says to be honest and truthful in regards to our "facts".
Jesus taught His followers to pursue honesty through clarity and performance. Say what you mean, mean it and do your best to do it. We're not going to perform a 100 per cent of that all the time, we know that, but any effort to redefine that blurs the reality Jesus led us to.