Djeggnog, I recall you (and the Society) used Hebrew “dor” of Ex. 1:6 as an example of the two groups equalling a “generation.” The Theological Dictionary of the Old Testament, vol. III, p. 174, has an interesting write-up concerning the meaning of the word “dor”.
For Hebrew dor, “generation” is by far the most common meaning, and less specifically “age.” With this meaning dor becomes a measure of time or a period of time. Like other ancient peoples, the early Hebrews dated long periods by lifetimes. They divided long periods of time into segments corresponding to the life-span of a generation. This is the meaning of dor in Gen. 15:16. The difficulty came in attaching numerical values to a generation, and ’arba` me’oth [400] in Gen. 15:13 were reckoned as 400 years (4 generations of a 100 years each). The idea that four generations equals 400 years, which lies behind Gen. 15:13, is undoubtedly based on an artificial scheme which assigns 100 years to a generation.
It seems to me that this would come closest to your understanding of “generation”. However, take note, above scriptures do place a 100 year limit on the word. It is also an open question to what extent this word would have influenced Greek koine usage.