So I was working with the structure block to create structures for future use. At one point a Wandering Trader wandered into the fountain I was creating just as I saved the structure while the with entities was on.

When I tested the placement of the structure else where on in my world (about 20 blocks away) when the structure loaded, with entities on a Wandering Trader appeared. I looked back at the original build and the wandering trader is there as well. Both have the exact same trades, but it was my understanding that there should only be one Wandering Trader in the world at a time.