Hi, sprawling_worm.
I'm glad you decided to reach out on the Apple Support Communities.. If I understand correctly, you’re seeing 3 devices when you check your account as outlined here:
Check your Apple ID device list to see where you're signed in
And, you’re seeing 5 devices when you check Find My as outlined here:
If your iPhone, iPad, or iPod touch is lost or stolen
If I have this right, do you recognize the two rogue devices in Find My? Is it possible they belong to family members in a Family Sharing group, or to friends that have shared their location with you? For example, when I tap the “Devices” tab in Find My, I can see all of my Apple devices as well as all the devices of everyone in my Family Sharing group that is sharing location. This article explains:
Share your location with your family
If they don’t belong to friends or family, are they old devices that you may have reported lost or stolen?
Best Regards.