I'll take a stab at answering Andi's question... at risk of stirring the pot.

Catalog authors have different methods of estimating values. Not all catalog authors have the same information available to them. One author may know of hoardes of a particular chip that may be unknown to another catalog author. Also; condition plays an important part in estimating values of chips.

There is not one standard catalog estimate resulting from all sources of information. It's purely a judgemental call on the part of that particular cataloger.

CNN news does not report the same news in the same manner that FOX does would be a good example. Both have different views of the same story.

Some folks like to rely on Ebay prices as guides. However, as I've stated several times in the past, ebay often times winds up to be a dumping ground for some folks who simply want to get rid of duplicate or unwanted material. Many ebay sales are purchased by others with the intent of re-sale at higher prices... which in turn often reflects higher prices in published catalogs.

Private sales of higher valued chips also enter into price estimates published in catalogs that the general collecting public may not be aware of which would cause one guide to reflect a different price than another similar guide. "Does Macy's tell Gimble's" is an old phrase that is still true today.