I'm assuming you don't have release-check (negative edge) on? Because usually if you tried a d1-corp charge, if release check was on you'd very often get an upwards lance blast instead.
Otherwise, yes, you have to tap down an additional time after the d1 since the inital down only counted towards that first move..
If release-check is on, you may be able to hit 1,D,2,D,B really, really fast for a reliable d1-grav pull
What will happen is you press 2 before D,B but fast enough so release-check will register the release of 2 as D,B,2- because it knows you can't cancel a D1 into a 2, it's just not a valid string, but D,B,2 is, so it will read that. You also won't have the problem of the second D not registering because the game interprets it as the D for the initial poke because it is buffer-separated by the 2.