If my memory serves me correctly the following would probably provide the most plausible explanation.
I seem to recall reading about copies of coins made for jewelry purposes that were of the proper gold content. They were adequate for the purpose of the wearer but would not fool a collector or dealer.
If you placed them side by side and examined them you could and would see the difference. However, if you simply did a gold content test they would match. Oftentimes they would be bought alongside genuine coins for melt.
I have seen bracelets and necklaces with these type copies. They included British sovereigns, US $20 & $10 (necklaces), and $5 & $2 1/2 (bracelets, cufflinks & rings. Also Austrian 20 (not sure of the denomination) Ducats,, French 20 Francs, and Mexican 50 Pesos.