In the beginning there was the Beechcraft Queen Air 65, it beget the Queen Air 85 which beget the Queen Air 88 (Which was a pressurized Queen Air 85, didn't make many of them.)
Then Beech replaced the Queen Air 88 piston engines with PT-6s and the King Air 90 was born. The stretched version was the King Air 100 which ended up with two versions, the original PT-6 powered and then an B-100 which had TPE-331 engines. Then came the 200 and the last version the 350.
However, where they come up with 1900 I really don't know, sorry.