Not sure if this qualifies. In Memento the character Teddy’s real name is revealed to be John Edward Gammell, meaning he is a “John G” and on the hit list.
How about Dr Who’s River Song? Her original name of Melody Pond is hiding in plain sight.
In the long-running musical The Phantom of the Opera, the Phantom had no name. But in the (bad) novel the play and various movies of the same name are based on, which was published way back in 1923 (so I think “early on” counts), his name is Erik.
In the animated movie Sing, one character refers to his grandmother as “Nana”, and it’s only when you see some magazines with her picture (she was a famous actress) you realize that her name was actually “Nana” (Noodleman).
In Neal Stephensons Cryptonomicon, Randy Waterhouse receives a strange email from the adress root@eruditorium.org. He assumes this is from the sysadmin of the eruditorium server. He answers and inquires about this mysterious persons name. “I already told you my name, but perhaps you didn’t recognise it as a name” is the reply.
Later it turns out the name of the email sender is Enoch Root.
The name of the Mother in How I Met Your Mother, Tracy, isn’t officially revealed until the end of the show. However it was actually subtly revealed much earlier when Ted meets a stripper with the same name and Future Ted shocks his kids by telling them, “and that’s how I met your mother!”
Mary Shelley’s original novel never gives the monster a name, although when speaking to his creator, Victor Frankenstein, the monster does say “I ought to be thy Adam” (in reference to the first man created in the Bible).… Within a decade of publication, the name of the creator—Frankenstein—was used to refer to the creature, but it did not become firmly established until much later. The story was adapted for the stage in 1927 by Peggy Webling,[5] and Webling’s Victor Frankenstein does give the creature his name.
So Shelly hints at it, then the stage play confirmed it. Sorta.