It only matters if it's in your account for warranty and recall purposes. If it appears in the Find function, you're good. If it bothers you that it doesn't show in your account, you can do as @BrĆ¼ZZi suggested and just re-register it.
If you go to your phone settings and tap your Samsung account and tap "devices", does it show? All my devices show, even one that says it's inactive (but I use it every day), yet one I haven't even turned on in a year is listed as active. Go figure. I'm not concerned as only one item is under warranty and the others appear in find my device. While you are in that setting, also tap on "registered devices" to see if it's registered. I find that there is a discrepancy between what shows as registered in my account on the web and in my account on the phone.
