Straight answers
Do colleges superscore the SAT?
Many colleges superscore, meaning they combine your highest Reading & Writing score and your highest Math score across different test dates into one total. But it isn't universal: some schools consider only your single best sitting, and a few ask to see every score. Each school states its own policy on its admissions site.
A concrete example: if you scored higher on Math in March and higher on Reading & Writing in October, a superscoring college would build a total from those two bests rather than from either date alone. That is why a retake can help even when the total score of the second sitting isn't higher than the first.
Superscoring changes how you should plan a retake. If your target schools superscore, it can make sense to go into a second sitting focused on shoring up the one section that lagged, rather than trying to lift everything at once.
It also affects which scores to send. At a superscoring school, sending multiple dates is generally safe, because the school is assembling your bests. At a school that reviews your single best sitting, or one that requires all scores, the calculation is different — which is exactly why the policy has to be checked per school rather than assumed.
Check the admissions page of each school on your list, and check it in the year you're applying. These policies have moved repeatedly in recent admissions cycles, and an answer from an older forum post or article is not a reliable source for a decision this concrete.