It wasn't until this happened that I remembered...

I've been playing this train game recently, and while clearing an event dungeon, I realized that the train given for this event is the same one I received before. I wondered why I was getting the same train again this time, thinking maybe it would be converted into other equivalent virtual items or upgrades after receiving it. But after claiming it, I found that it had the same name but different stats. So, I ended up with two identical trains, one being an N card and the other an R or SR card. It was this setup that made me remember... this is a mobile game, and having multiple versions of the same unit is quite common. This is fine, though; an extra train means increased carrying capacity. I also discovered that the tier reward train resets every 10 levels, meaning you can buy the same train multiple times, but its stats will vary depending on the level.