... How does one go about rebuilding bunkers in a manner that is true to C&A? What is the reference point (if there is one)?
Jason,
In all likelihood, it's no different from trying to emulate a Colt, MacKenzie, Ross, Tillinghast, or any other Golden Age architect's style for a given course.
Along with any available notes as shown for Colt and Alison, period photos and aerials are leveraged when and where possible to get a sense of the look and style for a given course. That look and style can vary from course to course. Tillinghast might be the perfect example of how this bunkering style varied.
Then the sympathetic restorations / renovations do their best to copy the look and style.
If nothing's available from the period to fallback on then it's completely interpretative while perhaps leveraging known content from other courses for a given Golden Age architect. It's probably a decision between the club and the engaged architect in terms of this.
Finally, chances are a club will also consider maintenance. In this regard, the club and engaged architect will review and make decisions for what can be supported and this can potentially affect how close the renovated/restored bunkering mirrors the original style. For instance, an original style of bunkering might have been more prone to say wind damage or water erosion, etc. Some modern best practices might be applied to counter these effects and that could affect the end result for the look and style.