TEPaul,
The flaw in your theory is that one must not only look at the face of the bunkers (in photos or in person) but one must look at the rear and sides as well to determine if the bunker got deeper, or if one side was built up, giving the false impression that the physical properties of the bunker are at a deeper depth.
And, you can't conclude from looking at photos or viewing in person, what the cause and effect are, you can only determine incremental changes.
In many cases, sprinkler lines where put in to encircle greens and often that caused a slight rise near the top of the bunker.
In some cases the area around the top of the bunker had to be built up to accomodate the lines and heads.
In other cases, the area around the top of the bunker was deliberately, physically altered, as was the top of the DA bunker at # 10 at PV.
Other times the crew, when edging destroys the top of the bunker, requiring it to be rebuilt. Prudently, the top is overbuilt, allowing margin for future erosion caused by edging.
You can't make the definitive statement on the cause of the change from a photo.
Core sampling can assist in determining the cause.
But, you can't attribute a specific cause to any change to the top of a bunker solely from a photograph of the bunker.
Unless, it's a picture, taken at night, of you, with a shovel, altering a bunker.
You have to determine the facts, first, then conclude.