Stuart,
lets go through this point by point.
First Simpson's sketches. Are you really not so sure he always drew AND always described frilly edges for his bunkers? If so I am very happy to post all his sketches I have and post all his text on how he wanted his bunkers edges. Sorry there cannot be any uncertainty about this.
Second the historic pictures. Some of them show frilly edges clearly, such as New Zealand, Berkshire and Spa, others such as Hardelot are more ragged. (In the case of Hardelot that might be because MacKenzie Ross was the man on the ground during construction. BTW we also use revetting in parts of the faces at Hardelot, but that doesn't exclude filly edges). However, none of the old pictures look as simplified as most of the bunkers look on Simpson courses look right now.
If we combine both points, I think we can safely say that:
a. we know with great certainty how Simpson wanted his bunkers to look, and that
b. virtually nowhere do his bunkers now look like that anymore