Importance Of Scotts Catalog Version?

In terms of identifying US stamps from 1840 - 1940 is there a particular reason one should have a newer version of Scotts? The one I have currently is 1973 Vol 1. I've ordered the 2009 to help with more recent things. Do I need to get the Classic Specialized Catalog also?

If identification is your issue then you do not need a newer catalog. That being said, you would probably be rewarded nicely if you could acquire a cheap U.S. Specialized catalog. It can really be helpful in identification issues and in dealing with philatelic materials not covered in the Standard edition.

For US stamps, if you have the Scott US Specialized Catalog, there is no need to get a Scott Classic. Everything US in the Scott Classic is also in the US Specialized, and the latter has far far far more information and can be purchased for half the price.

I think it is wise to get a recent catalog (at least within past 10 years), as there have been some listing changes for the US since 1973. The 2009 should be good. Avoid the 2005 US Specialized (inaugural color catalog for this volume).

Also avoid ALL the 2011 volumes first print run (current printing) that have already been release (I-III, at this point) -- major boo-boos; for just the US alone, Scott has already issued a full page errata sheet. Looks like the 2011 set is going to surpass the 2006 set in the disaster rankings in terms of listing errors. At least in 2006, they could blame the colorization process.