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Searching for Comments to Proposed Federal Regulations
Have you ever tried to find the comments that influenced specific federal regulations?  The Reference Question of the Week recently addressed that issue.  The answer can depend on the time at which the regulations were adopted.    In the question addressed by the Reference Desk, the regulation at issue was adopted in the 1970's. 

Comments, along with the agency’s responses, are either listed in their entirety or summarized, depending on the number received. The actual comments for your rule were probably put in boxes and stored in a government warehouse, but are probably not indexed or accessible. In the late 1970s a federal agency that had just finished a big rule-making handled their comments that way. (If you’ve seen the first Indiana Jones movie, I always picture them sitting right next to the lost Arc of the Covenant.)

The Reference Desk suggested a FOIA request, a search of periodicals from the time period in question and records of litigation challenging the regulations. 

The time period was determinative. As the Reference Desk pointed out: 

If only this rulemaking were happening today. Regulations.gov allows public access to the actual comments received by the agency. As more agencies move to electronic rulemaking, more of the process will be transparent.