In the 1990s Common Dolphin was split into long-beaked and short-beaked forms and counted as two different species. Currently they are lumped. According to Bernardo Alps (see below), the work to re-split them is ongoing. To tell them apart, go to the 45 minute mark of his talk on the LA Birders website.
In Oct 2022 he did a talk focused on Southern California titled “marine mammals for pelagic birders,” but the ID tips apply to entire West Coast. (He also cleared up a mystery for me. As a young birder, I distinctly remember pilot whales being reported from pelagic trips, yet since then I have never seen them in California. Apparently gill-net fishery and perhaps an El Nino year did them in just as I learned about them. Now they are gone.)
He has very specific tips on field ID of the two forms / species of common dolphins. See them now, count them later — like money in the bank.
Talk is archived on YouTube for free.
If that does not work, go to LA Birders at https://www.labirders.org/
and look for their webinar series.
Charles Hood / hoodcw at gmail.com