How does Apple's dual card distinguish short messages?

In the current version of iOS, Apple does not have a mechanism to classify short messages according to mobile phone cards, but it can distinguish them in other ways. Here's how to distinguish them.

1. First unlock iPhone 12, open the SMS APP on iOS 13/ 14, and click the SMS you want to view.

2. Click the sender number above, which is the red box area in the figure.

3. Click the "Info" icon among the three icons in the drop-down box.

4. At this point, it shows that "XXX" is being used in this conversation. You can see which number received the message.