Optimized how analysis work

I notice that every time you use analysis after match. Chess.com keep calculating everything from the scratch. For example if i play Ruy Lopez and process to play 5 books move along with my opponent. These must by a thousand of game start with those particular 5 moves in database. But chess.cok computer is keep running the calculation over from scratch then it offer the best of 14 moves calculation and the best of 16, 18 and so on until it reach the maximum capacity which is 20 moves. I imagine that the will be alot of repeated calculation like that in 1 month which cost alot of time and computer process and therefore for cost alot of money. Shouldn't it programmed to only offer the best of 20 moves which already existsed in the database? What do you think about it