Verlinden himself didn't do all his homework on this either, so don't worry about it too much. While not identical to the model, this may very well be the bunker Verlinden styled his from;
Verlinden has been known to cut a few corners while producing their products. I think the same may apply here. Fittings like stove pipes, ventilation openings, the ladder on the side, doors, etc., are all missing from the kit. The shape of the bunker is somewhat simplified too.
Notice how the sand has eroded away from around the base of the bunker in the above photo. This would have been completely covered with sand 60 years ago. Many bunkers left at Normandy have completely washed into the sea or toppled over from erosion around their bases, here is just one of many in this condition;
I built this kit too. I also didn't bury mine in the ground either.
I didn't know it should have been buried until long after I built it. I'm planning on scraping the diorama and rebuilding it in a different setting, this time setting it in the ground as it should be.
What else are you planning to add to your's? Some figures perhaps? Looks good so far!