Even though I own a recent Scott Classics Specialized catalogue, I just purchased a copy of an original 1941 Scott on the assumption that it might be useful, too. Although I haven't put the '41 through a thorough workout, my initial impression is that one of these catalogs contemporary with the album is worth acquiring. To begin with, there is a closer correspondence between the listings in the '41 and the Scott International Volume 1 album, starting with the order and name of the countries. More importantly, the years printed in the album correspond much more closely to those in the catalog making it faster to identify multi-year sets with many values. Even seemingly small things like the names of colors are more likely to match. I'm dwelling on the matching because I'm penciling in catalog numbers for every space in the album and so ease of identification is a great timesaver.
And while I'm only beginning to discover these, there are discrepancies between the album and the current Classics Specialized that earlier catalogs can help clarify. For example, the Scott International album has spaces for Angola both Scott 129 and 130. While both stamps are in the '41 catalog, only one is in the latest Classics Specialized.
The biggest problem is that the 1941 edition still isn't complete for stamps issued in 1940. While many if not most of the 1940 stamps are in the Addenda, one still has to remember to check the catalog in two places (actually three as there is a Tentative Issues section, too, for questionable stamps that might or might not make it into future editions). My guess is that the 1943 edition might be the best one for Scott International collectors to acquire (the 1943 is the edition specifically mentioned on the title pages of the Scott "Blues" published in the 1940s and 50s) and I'll be on the look out for an affordable copy of that one.