I got curious, so I checked. Per the Disraeli Gears site, EDCO was a Swiss bike component manufacturer dating from the early 1900s. Per Disraeli, EDCO derailleurs apparently were "top-end Simplex and, later, Sachs-Huret derailleurs branded as EDCO".

The company appears to have gone under in the late 1980s, but has been resurrected and now again makes bike components.

Perhaps [MENTION=20650]T-Mar[/MENTION] or [MENTION=158672]FBinNY[/MENTION] can provide more info about EDCO.