You know, the second hand stores in my neck of the woods have quite a few of his juvies-- multiple copies too.
I pretty much take it as a given that any dates explicitly given in an SF story should be quietly ignored. Experienced authors generally know enough not to give them at all, and the stories generally hold together quite as well without that information. So sure, ignore the dates in the Future History.
Other than that, the biggest inconsistencies are of the form that new scientific advances were made over the course of Heinlein’s career, and he was trying to keep up with them. For instance, nuclear power works differently in, say, “Blowups Happen” and “The Long Watch”, because not enough was known about nuclear power (to the layman, at least) at the time of the former story. So in the later stories, he doesn’t say much about the tech of nuke power, but what he does say is more consistent with “Armstrong alternate timeline” physics than with “Leslie LeCroix timeline” physics.