I was able to check mine with a simple magnet, I do not have an electromagnet or any access to one, but I can say definitively in the case of a night of the long knives dated ring and a 1940 dated ring, they do not react at ALL to a magnet. 40 has of course lighter engraving minus most of the name, long knives is complete inside the band. I put the magnet to both inner bands, no reaction or pull. These are both well known originals.