You specifically mention that the ages of the fathers following Shem is shortened by 100 years. So, I felt compelled to look at comparison translations. Beginning with Arphaxad, out of 35 translations of the Scriptures, there is one, and it is the Septuagint translation that allows that Arphaxad was 135 years old when he had Shelah. Now, I believe myself to be a reasonably wise man with pretty normal thought processes and it comes to my mind that there must be a reason, that out of all these people who have given of their life's work to correctly, in their understanding, translate the Scriptures, that only one out of 35 adds the 100 years.
The 35 translations you refer to are derived from the Masoretic Text (MT) version of the Old Testament. This is the version of the Bible I was brought up on, and still use (specifically the King James Version). Bible Gateway provides 60 English translations of the MT. Most of them are closely translated. But a few of them, like the Amplified Bible, adds whole phrases inserted between verses (see Rev. 22:18–19). These 35 or 60 versions of the Old Testament come from a group of Jews known as the Masoretes between the 7th and 10th centuries AD who transcribed Hebrew into Hebrew. It is not the original text of the Hebrew Bible: the original text has never been found. The oldest extant manuscripts of the MT date from around the 9th century.
The Septuagint (LXX) is the earliest extant Koine Greek translation of the Hebrew Old Testament. The LXX was translated by the 2nd century BC and was in wide use by the time of Jesus and Paul because most Jews could no longer read Hebrew.
Since the invention of the Gutenberg printing press ca. 1453, production of the Bible has been easier but also more frequent, with more personal taste. Lets take Daniel 9 for example. The 1599 Geneva Bible (used by the Puritans on the Mayflower) on Dan. 9:26–27 says,
"And after threescore and two [62] weeks, shall Messiah be slain, and shall have nothing, and the people of the prince that shall come, shall destroy the city and the Sanctuary, and the end thereof
shall be with a flood: and unto the end of the battle it shall be destroyed by desolations.
"And he shall confirm the covenant with many for one week: and in the midst of the week he shall cause the sacrifice and the oblation to cease, and for the overspreading of the abominations, he shall make it desolate, even until the consummation determined shall be poured upon the desolate."
Now compare with the Amplified Bible:
"Then after the sixty-two weeks [of years] the Anointed One will be cut off [and denied His Messianic kingdom] and have nothing [and no one to defend Him], and the people of the [other] prince who is to come will destroy the city and the sanctuary. Its end
will come with a flood; even to the end there will be war; desolations are determined.
"And he will enter into a binding
and irrevocable covenant with the many for one week (seven years), but in the middle of the week he will stop the sacrifice and grain offering [for the remaining three and one-half years]; and on the wing of abominations
will come one who makes desolate, even until the complete destruction, one that is decreed, is poured out on the one who causes the horror."
See how a newer translation can add words and change meanings? The Septuagint is older, and could even be more accurate, since it is based on an older copy of the Hebrew.
Also, the Masoretic Text states that the Israelites sojourn in Egypt was 430 years, and presumably enslaved there for that long. The MT version of Exodus 12:40 says,
"So the dwelling of the children of Israel, while they dwelled in Egypt,
was four hundred and thirty years."
But the Septuagint says, "the sojourning of the children of Israel, while they sojourned in the land of Egypt and the land of Canaan, was four hundred and thirty years."
If the Masoretic Text is used, the four hundred and thirty years (Ex. 12:40) would begin when Jacob reunited with Joseph in Egypt, but noting the lifespans of Levi, Kohath, and Amram (Moses' ancestors), each of them would have had to begotten their sons an average of 5 years before dying at ripe, old ages of about 136. Since it was difficult for Abraham to have a child when he was one hundred years old (Gen. 17:17), it is highly unlikely that Levi, Kohath, and Amram all begot children at about 131 and then died 5 years later.
Using the Septuagint, the four hundred and thirty years began when Abraham entered Canaan with Lot. This would make the sojourn in Egypt only two hundred and fifteen years, which agrees with Gal. 3:17 in either translation, and the enslavement of the Israelites about one hundred twenty-five years (Ex. 1:6–11). God called Abraham in 2020 BC, whereupon he left and entered Canaan at age 75 (Gen. 12:4). Twenty-five years later he begot Isaac (Gen. 21:5), and sixty years later Isaac begot Jacob (Gen 25:26). Jacob was 130 when he entered Egypt with all of his children. So doing the math, 25+60+130=215 years, and 2020 BC–215 years=1805 BC. And since they were in Egypt AND Canaan a total of 430 years, all of the Israelites were in Egypt for 215 years, until 1590 BC. 215 years between Canaan and Egypt, and 215 in Egypt.
Jacob was 85 when he had Levi, and Levi lived 137 years (Ex. 6:16). Levi's son, Kohath, lived 133 years (Ex. 6:18). Kohath's son, Amram, lived 137 years (Ex. 6:20). Moses was 80 when he spoke to Pharaoh at the time of the exodus (Ex. 7:6). So working backwards from 1590 BC 80 years to Moses' birth (1590+80=1670 BC), it provides for 180 years for the 3 generations from Kohath to Moses (1850 BC–1670 BC=135 years). Sixty years was a prime age to have children back then. If you use the Masoretic Text, each ancestor had their child at about 131 years old, then died 5 years later. This is only for the purpose of a fun exercise, if you ask me. But someone may want to know the true age of the earth, in contrast to scientists who try to extrapolate past 7,000 years ago, without knowing the atmospheric conditions of an antediluvian biosphere, and assuming the flood didn't happen.
I tend to trust older translations of the Bible to newer ones.
