... but then say a sentence later 'That is also cumulative and either way...' ???
Yeah I think my organic cache had just gotten full after the previous sentence. Ha.
Here's a picture, even though I think you have a handle on it I don't want to mislead later lookers.
Attaching a breadboard to the end of face glued top (A) isn't something I would suggest, but if you do make sure the breadboard is flat sawn with the long grain perpendicular to the top's end. And don't rout a groove into the breadboard edge - rout the groove into the end of the face-glued top and put the tongue on the breadboard.
The way the grain's oriented on a face-glued top means that it'll expand and contract in height, and if the breadboard edge had the groove then the tongue of the top could theoretically expand enough to asplit the grooved bredboard apart to some degree, or even expand enough that it wouldn't allow the slippage a T & G breadboard is designed to give which could also cause splits.
But even with the groove on the edge of the top, if it shrinks enough it could clamp down on the tongue enough to prevent the desired slippage too. So for this reason I don't like the face-glued tops for use with breadboards. Even by incorporating large enough tolerance in the T & G you then have to find a work-around for a sloppy and loose breadboard.
Some may say I'm making it too hard, but if you're building furniture might as well try to eliminate as many potential problems as possible no matter how small.