Magicians coins aren't designed to be fed into vending machines or coin counters - they fool the eye, not the machine - so they usually won't be correct weight. There's always an air gap in between the two halves of the coin, so unless there's extra thickness, the weight will almost always be lighter.
As for the thread-bumper's question: multiple people have been making these, for decades. The dates are going to be random.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis