In fact, sometimes things work in the opposite way: what was "obvious" earlier in time becomes less obvious later in time. An example in Civil War history concerning the actions of JEB Stuart and George Armstrong Custer on July 3, 1863 at Gettysburg is illustrative.
Pickett's Charge happened in the early afternoon of July 3, 1863, and did not end well for the Confederate forces. Some people, recognizing the brilliance of Robert E. Lee in May 1863 at Chancellorsville, have difficulty accepting that the same Robert E. Lee ordered Pickett's Charge, which likely had a very low probability of success. A recent book by Tom Carhart suggests that there was a master plan by Lee, involving an attack by JEB Stuart on the Union right (Confederate left), which proves that Lee's thinking was not as bad as might be inferred from the outcome of Gettysburg. Stuart's attack was stopped by Custer, which "stop" thwarted Lee's master plan. This idea of the master plan was presented as a novel theory in 2005, and many reviewers have acknowledged it as a novel theory.
Flash back to the year 1878. Gettysburg happened 15 years earlier, and Custer died at Little Big Horn two years earlier. William Brooke Rawle, a participant in Gettysburg, wrote: "It was OBVIOUS that he [Stuart] intended to accomplish this [surprise in Federal rear] by way of the Baltimore Pike and the roads hereafter described, SIMULTANEOUSLY with Pickett's attack in front." There's that word "obvious." Thus, the theory that was novel in 2005 was obvious in 1878. As Einstein said, opinions about obviousness are to a certain extent a function of time.
But, was the theory correct? Priority is one thing; evidence is another. Rawle suggests that Stuart's goal was blocked once Hampton's and Fitzhugh Lee's troopers entered into open ground, and were seen by Union forces. Rawle neglects to mention that Stuart's force fired cannon PRIOR TO any engagement with Union forces and not directed at any Union forces, not exactly what one does when planning a surprise. Sometimes, when one advances an "obvious" theory, one omits mention of facts which make the theory not obvious. Carhart mentions the cannon shots, but asserts they were a signal to Lee. Carhart did not mention Rawle, or a book published by Walker a few years before the book by Carhart that advanced the same theory.
Stuart himself wrote: "Had the enemy's main body been dislodged, as was confidently hoped and expected" [by Pickett's charge] "I was in precisely the right position to discover it and improve the opportunity." One can infer that Stuart planned TO BENEFIT FROM THE RESULTS OF Pickett's attack, not to help CAUSE the results.
Confederate Major H.B. McClellan wrote: Stuart's object was to gain position where he would protect the left of Ewell's corps, and would also be able to observe the enemy's rear and attack it in case the Confederate assault on the Federal lines were successful. He proposed, if opportunity offered, to make a diversion which might aid the Confederate infantry to carry the heights held by the Federal army.
Firing cannon shots which alert the enemy to your position is consistent with a diversion, not a surprise attack.
Whether the theory was advanced in 1878 or in 2005, it's not "obvious" unless there are facts which support it. The whole deal in the CAFC opinion in KSR v. Teleflex was not about whether the invention was "obvious," but whether the underlying facts were written down. When one combines bits and pieces from a number of prior sources, it is incumbent to show why the bits and pieces were combined to prove that the mosaic renders the later thinking "obvious." Opinions about obviousness are to a certain extent a function of time because the recognition and analysis of the underlying facts can be a function of time.
As a separate point, most people would expect that our ability to gather facts to determine obviousness would be greater for more recent events, because recent events are more thoroughly documented on the internet. This is not necessarily so. In the Gettysburg example, the work of William Brooke Rawle from 1878 is well-documented on the internet. In contrast, the rather interesting "Vai's View" by Vai Sikahema, entitled "Rutgers is Wrong", which appeared less than one year ago, has vanished from the internet after the successful football season by Rutgers. Things that go up on the internet can easily be removed from the internet. See Internet Publishing: Online Today, But What About Tomorrow Or Where Have You Gone, 406,302?