Fleet Variants
Alaska flew the 737-200 as a separate fleet from their CFM powered brethren. Probably a good idea as those -200s had gravel kits, combi cargo doors and flew into unpaved airports.
They operate the 737-400/700/800/900/-400 combi and the freighter all as one fleet model. Oh yeah, there are also variants as to winglets or no and multiple cockpit configs.