In your setup: not possible.
The indication that a file is (or is not yet) imported is stored within darktable, not on the SD card. As your two versions each have their separate database, one cannot know that the other already imported a given file.
And as @pehar already pointed out, you can’t synchronise (or share) the database between versions.
For basically the same reason, you may not be able to use a 4.3 edit with dt 4.2.
If you can live with using only one dt version, you might be able to set up a system where the darktable data are on a single disk or partition, shared between the two systems.