In Bereshit 13:1, Negev is meant to mean the south of the Land of Israel (according to Rashi), because Abraham was going from Egypt to Israel and otherwise wouldn't make sense.
וַיַּעַל אַבְרָם מִמִּצְרַיִם הוּא וְאִשְׁתּוֹ וְכָל אֲשֶׁר לוֹ וְלוֹט עִמּוֹ הַנֶּגְבָּה
And Abram came up from Egypt, he and his wife and all that was his, and Lot with him, to the south.
. . .
But in Bereshit 13:3, Negev means just south (also according to Rashi), because Abraham was going from the south of Israel to the North.
וַיֵּלֶךְ לְמַסָּעָיו מִנֶּגֶב וְעַד בֵּית אֵל עַד הַמָּקוֹם אֲשֶׁר הָיָה שָׁם אָהֳלֹה בַּתְּחִלָּה בֵּין בֵּית אֵל וּבֵין הָעָי
And he went on his journeys, from the south and until Beth el, until the place where his tent had been previously, between Beth el and between Ai.
How can Negev change meanings like this?