This sounds less like a Signal problem than an information organization problem. Signal can only show what's in its datastore (your contact list).
I just checked on Android - if you try to add someone to a group chat, it shows their name and profile pic.
One potential Signal-side wrinkle is that it allows you to add people to a group chat who are in another chat you're in, but who aren't in your contacts list. There are strangers I was apparently at a dinner party with years ago who are eligible to be added to a group chat. If Jeffrey Goldberg has his Signal profile name set to JG and he wasn't in Mike Waltz's phone with a more specific name, that could lead to this mistake.