AN is right serrento valley is not a “community” as it does not appear on the city map, and it is part of Mira Mesa.
Although if you look at the various communities, it seem like independent communities are often morphed together when it comes to general usage. For example, Carmel Valley encompasses Del mar Mesa, Torrey hills, Pacific Highland Ranch. RB is the same way, it has taken to mean Carmel Mountain Ranch and Sabre Springs. While Scripps Ranch has fully absorbed Miramar North and give a few years it’ll do that to Rancho encantada as well.
The names are fluid. And if things make sense, then separate communities kinda disappear under a single larger entity even though the city still brand them as separate. On the other hand, the reverse can happen too. There is a separate identity with serrento valley and I doubt MM will be successful in “reclaiming” it so to speak.