Parsha: Lech Lecha, Galut Mitzrayim - 400 Years or 210 Years?‏

Here is a simple approach to what appears to be a big s'teerah between the 400 years in Mitzrayim as per Torah Shebichtav, vs. the 210 years as per TSBP.
[Note: I'm not addressing the case of 430 years, but one can extrapolate an answer from this approach]

Rashi [Lech Lecha 15:13] suggests that the 400 years in a "Land not theirs" commences with the birth of Yitzchak, and that the actual descent to Mitzrayim actually comes 190 years later.

Extrapolating from Rashi here is my approach:

There are "2 dinnim" re: Egypt

1. The physical Land of Egypt
2. The extended Empire of Egypt.

Background:
Modern Archaeologists consider the Ancient Land of Canaan during that era as under the influence [Suzerainty] of the Egyptian Empire, perhaps similar to Poland used to be when it was under the Soviet Sphere of influence.

So, in a sense, during those first 190 years, the Avot were not in the physical Land of Egypt, yet the galut of the Empire of Egypt indeed did start earlier on - because Canaan was under the Social and Political Influence of Egypt, and by extension they were in a "Spiritual Galus Mitzrayim."

And so both figures work.
210 years in Physical Egypt
400 years as subject to Egyptian Social Mores.

Kol Tuv,
RRW