Mike,
Here is some further evidence of changes.
From 1925:
Even a cold winter is not preventing the Oakmont Club from preparing for the coming of the great amateur stars during the approaching season. Emil Loeffler, the course greenkeeper, under the guidance of William C. Fownes, Jr., started early last summer to prepare the course, putting in new tees and changing many of the greens, so that those who played over Oakmont in the 1919 championship will see a course vastly different from that which greeted them when the title event was staged here five years ago. Number thirteen green, which was picked by "Chick" Evans as the thirteenth green on an "All-American" course some time ago, is among the greens being changed, Needless to say, it is not being made easier. The number six green, difficult enough in 1919, has been remade, and it is now said to be one of the best holes in the country. The same is true of number seven. This green was rebuilt early in the season but after being almost finished was deemed not good enough and was torn up again. Now it is said to equal any number seven hole in America. Other changes are slated between now and the time for the big title tournament that will make the course, already considered an extremely difficult one, the equal of any golf course ever constructed.
From 1927:
The course has undergone some big changes since the amateur championship was played there in 1925. The old
sixteenth hole has been eliminated and a new hole built. There was fault found with this old hole by some of the players, who pronounced it a bit unfair. The green was of the hog-back variety and it was difficult to hold your tee shot on it. The hole measured 230 yards and the safest way to approach it was to play your tee shot, short, and slightly to the left, permitting your ball to trickle on the green. Often a well played shot onto the green would be penalized, as it would not stick on, but would land in the traps and bunkers on the sides or rear.
The new hole is a big improvement and is now one of the sportiest one shotter on the course. The tee has been moved back and elevated, while the green has been brought forward. There was no change made in the distance, and it still measures 230 yards. The rim of the green has been built up and there will be no difficulty in holding
your tee shots. The green is severely trapped and bunkered, and a poorly played shot will be penalized and there
will be no escaping with impunity. It will be all carry from the tee and an accurate shot will be rewarded. Another important change is the one to the fifteenth green. A new green moved back 40 yards has been built and it calls for a full iron on your second shot. The hole measures 470 yards with the new green. This green is also guarded with deep traps and bunkers on the sides and rear. A new tee to the eighteenth hole will add 20 yards distance and make it a lot harder, this will make a fine finishing hole.
(Oakmont played at 7,000 yards for The US Open that year)