I think Oda’s going for a different literary work: The Vicomte of Bragelonne: Ten Years Later by Alexandre Dumas, or more specifically, the final third: The Man in the Iron Mask.
For those unfamiliar with the story (even I’m pretty sure I maybe saw part of the Leonardo DiCaprio movie and maybe an episode of Wishbone, even though it occurs to me a lot of you might be too young to know what that show was) the basic idea is that the titular character is the twin brother of the King of France. Now there was a REAL Man in the Iron Mask but no one knows who they actually were (royal twin or not) but for the sake of this theory we’ll be going with the Dumas story.
Sanji being in that mask, as some have pointed out, is probably meant to keep him from being recognized as a member of the royal family, and since he’s a quadruplet of all things that’s especially risky. So why not kill him?
I’m thinking Judge planned on keeping Sanji down there indefinitely just in case a situation like this came up. And for that matter … we don’t know how long Sanji was in there (both the mask and the cage/jail cell).
In 832, Reiju explained it had been 13 years since she spent time with Sanji, but it’s only been 11 years since Zeff came into the picture (Sanji was 10 during the starvation flashback). That’s two years to go from “not spending time with Reiju” to the sinking of The Orbit. Yeah, crossing the Red Line as a kid would take a while, I get that, but taking a look at volume 7 (sorry no pictures for this one) … I don’t think Sanji was on that ship very long. The dialogue feels like the cooks are still in the process of introducing themselves to him - maybe not “first day” introduction but he’s still a newbie at this point.
My point is that “not spending time with Reiju” doesn’t mean he left home right away. He could have been in that mask for a while, up to two years when you consider Germa Kingdom is mobile - he could have escaped while they were in/around East Blue and found his way onto The Orbit from there.
- Oda has said that if Sanji were from the real world he would be French, and The Man in the Iron Mask is a story about French royalty written by a French author. - Duval is initially named “Iron Mask Duval” and hid his face because of Sanji’s wanted poster. Other than the fact that he, you know, tried to kill Sanji when they first met, his use of the mask to hide his face might have REALLY rubbed Sanji the wrong way.
And … oh man this chapter guys, this chapter. Everyone just … just go find something fluffy with Sanji in it okay? Okay.