Curse the Blue Book again. There is no such thing as a Series 70 Commander so there cannot be a Pre-70 Series Commander. The Commander and Combat Commander never got the collett bushing that is the distinguishing feature of the Series 70/Mark IV Colts, and the reason for the name change when the collet bushing feature was introduced in 1970. I think the confusion arises from the fact that a new serial number range was also started in 1970 that begins with "70." That still does not make the guns Series 70/Mark IV pistols because no Commander ever had the collett bushing.
Another point is that the nomenclature "Lightweight Commander" was not used until after the Combat Commander came out, since before that, there was only the Commander that came out in 1950, with no adjective "Lightweight" to qualify it.