I was writing eBay listings for trains I used to collect, but don't want anymore and I found a few odd 4-wheel cars.
First is a common 902 peacock gondola. Nothing special about it.
But if you look at the other side, you see it has three Lionel plates and only one number plate:
I call this a factory error. The person putting the plates onto the car, put the wrong one on.
Here's a different car:
This is an uncataloged 807 caboose from about 1935 with brass number plates and nickel Lionel plates. You can find this same variation in the 804 tank car.
I think this is more of a clean out. The Lionel plates went on everything. They'd certainly use the brass ones up.
Terry