I find it funnier that none of Undersides know Joe's first name. I mean, here they were giving him their legal civilian names, and that absolute creature just goes "You can call me Joe.", and to this day not even their thinker figured out that he hasn't given them his name. We at the point where Danny Hebert probably knows about Apeiron's civilian identity more than Tattletale, despite her making panicking about him 24 hours a day hobby.
I can see a meeting between Joe, Aisha and Brian, and the most surprised Brian sounds is when he asks: "Wait, your name is Jozef?!". Grounded stuff hits harder than ungraspable problems and all that.