Can you maybe tell by candling? The light might look different as it passes through shells of different thicknesses.
If you want to test the idea, you can candle a bunch of eggs. If you cannot see any differences when candling, then of course it will not work. If you do see any differences you can sort them into separate cartons or piles, then crack a few to see if you were actually seeing a difference in shell thickness or whether you were actually seeing something else.
I have never tried candling to check for shell thickness, so I do not know whether it would really work or not. If you try it, I would be curious to know what you find out.