I don't remember the reference in the Snowball but it wouldn't surprise me.
The Walkers Manual is a great book, I have the 03 edition, and the 1999 Penny Stock edition. I've found that a lot more of the stocks in the Penny Stock Manual aren't tradable anymore, many more than the unlisted stocks. I think the reason so many unlisted stocks are still around is that they can operate under the radar without much of an issue.
I think most people who've gone through the book and looked at this companies would agree with your assessment, this is an inefficient area of the market. Not only is there little to no analyst coverage, most of the time there is little to no information period. Most of the time you need to buy a share of the company and then call (and usually talk to the CFO) to get an annual report mailed out.
This is a very cool area of the market, I'm having a lot of fun researching these companies. You need to be innovative to find information, real estate tax records, creative Googling. This isn't your standard look at a few metrics and move on type of deal.