WHAT ARE "B-MODELS"?
This term was used by Bjarne Panduro Tveskov (senior LEGO Space designer in mid-80's/early-90's) in THIS interview, describing models pictured mainly on rear side of LEGO boxes in 80's/90's, which are basically some different possible builds (without building instructions!) from the exactly the same pack of bricks as the main model set (or in principle: "Let's see what else we can build from the sets bricks only").
So that said below are some of my interpretations of those...all the LXF are, of course, mine...