The problem with the Gerber ratings is that they don't take the condition of books into factor. For instance, if Book A has approximately 45 existing copies, but most of those were warehouse finds that grade VF and above. However, Book B has 70 existing copies, but only 3 or 4 them are considered HG. If someone is searching for a decent HG copy, then the Gerber guide can be misleading.
That's why I hope someone puts together a guide that rates the "Availability Factor" of a book over the past 10 years. This factor would range from 0 to 10 depending on the number of available copies, how often they show up in the market place, and in what specific grade. If only 30 copies exist of a certain book, but their owners have been hoarding them for the past 15 years, then the average buyer should be aware of that.
If I'm trying to complete a certain GA run in 6.0 and above range (let's say for Batman #60 to #70), and Gerber shows a 5 rating for all these books. Let's say I purchase Issues #60-69 at guide value, but pass on Issue #70 at 1.3X guide. However, I spend the next 2 years looking for a decent copy and it doesn't show up, while the rest of the books seem plentiful. I'd start kicking myself for not having purchased the book back when I had the chance. Perhaps, Gerber was wrong on the number of existing copies for this book, perhaps they were all in low grade, or perhaps the cover is so nice that none of the original owners wants to part with it. With all do respect, all of these scenarios would rate the same for me if I'm trying to complete a run.
An "Availabilty Factor" guide would be much more helpful to the average collector than the Gerber guide.
Sorry for my