Law being a comic book nerd is great, though how did stealth black end up as a fictional character? Sanji got disowned as a kid. When would there have been anyone touting the #3 battle suit, let alone why would the suit even have existed back then? Did Judge make an invisible suit to represent the son that disappeared? Or did the comic writer make up the #3 character to fill the gap in the lineup, and Judge liked the idea and copied it for Sanji? I mean there's so much to assume to reach a point where the family preemptively went through the hassle to make a custom raid suit for the son they were, just days prior, so ready to sacrifice to Big Mom. I suppose we're not supposed to think about that too much, eh?
The idea is that X-Drake (and maybe Hawkins?) are on their way, and since they are both members of the worst generation, they would likely know who Sanji is. Truthfully, Luffy, Law, and Zoro have all been identified already, so I'm not sure why it would be a shock for them to find Sanji, but I think they're still banking on the enemy thinking it's some random encounter and not part of an elaborate coup.