In The Urantia Book the revelators are making clear that the nature of science itself is revision. Until the physical creation is complete and is established in light and life an eternity from now, evolution will always be a part of the eternal plan.
There is no science on this world which will not at some time stand in the need of revision and that includes the science explained in The Urantia Book.
You're reading now about the limits of revelation. Most likely, if there were no limits placed on what the revelators could have revealed, had they told what they know, it would be meaningless to us. So they explain what we can understand, knowing themselves that it is incomplete, partial, and will stand in need of revision. That doesn't mean it's erroneous; it just means that short of God, everything evolves.
Yes, it says that in a few short years many of the statements will be out of date. What does "a few short years" mean to the revelators? You've probably read that although Lucifer was interred about 200,000 years ago in our time, it's like it happened a few seconds ago in heavenly time.
You say: "This sounds like a huge disclaimer." It is a disclaimer that again says, short of God, nothing is unchangeable. They're warning us not to assume that the revelation is infallible, that the book is not to be worshiped, that we're being given as much new knowledge as we're capable of absorbing at this time in our history.
Thanks so much for this important question.