I can add a little history on the Cobra, and will include my rebuttal of the "issue" term used by the "Blue Book." The number of "issues" the "Blue Book" lists do not correspond to the significant changes in the Cobra. Colt75 has outlined the chambering and barrel length variations, which I will not address.
The Cobra has a much shorter history than the Detective Special because it did not exist until Post-War. The Cobra was introduced in 1950 as an alloy-frame version of the Post-War Detective Special, already in its Third Generation by that time. These early Cobras had the “Dual Tone” finish and plastic stocks. I would call these guns "First Generation." The plastic stocks were changed to wood in the mid-1950s, and the “Dual Tone” finish was dropped. I do not consider the stock material or finish change as another generation, but some might. In 1966, the butt frame was shortened, which is Second Generation. In 1973, a year after the Detective Special got the shrouded ejector rod, the shrouded barrel was introduced on the Cobra, which I count as Third Generation. The Cobra last appeared in a Colt catalog in 1978, and was absent from the 1979 catalog.