For most generations of Genesis, years of lives can be found; the exceptions are those in the middle, those of Shem through Nahor.
Adam through Noah have lifetimes noted (Gen 5:3 – 31, 9:29). Next, those from Shem through Abraham’s grandfather Nahor don’t (Gen 11:11 – 25). Finally from Gen 11:26 – 50:26, extents of lifetimes from Abraham’s father Terah through Joseph can be found.
Why might that be?
Note: While one explanation might have been that different authors give different notes, Nahor and Terah are right next to each other. While one has his lifetime noted the other doesn’t.