Well, The Man Marked By Flames most likely counts, since that's not really a name, more of a title or epithet. And we're not sure if that's The Twelfth Man or not.
Also, the Gorosei. Sure, we knew they were the Gorosei, but we didn't know any of their names for DECADES. Those should count.
At the time, I think we got silhouettes for some of the Seven Warlords before knowing all their names? Someone might have to fact-check me on that. It's been a while.
Same goes for the Yonkou. I honestly forget if Kaido or Big Mom were originally named before we saw their silhouettes or not.
Again, maybe some of Blackbeard's crew? At least when some of them were first broken out of Impel Down. I forget if we saw them before we named them.
Arguably, Joyboy and Nika count. Those may or may not be their real names. Again, more titles or epithets, maybe.
The Going Merry's klaubatermann. We didn't know it's name or what it was when we first saw it on Skypeia. So, maybe that counts?
A lot of Rock's Crew. And the zombies on Thriller Bark, for related reasons. We still don't know for sure a lot of their names.
The majority of the God's Knights.
I'll admit, some of these stretch the definition of "silhouetted". And for most of these, we at least know SOMETHING about them, even if it's just what group their associated with.
The Twelfth Man really is up there for characters we don't know anything about when we're first introduced to them.
