Welcome, BDuff! Hope to see many more thoughtful posts from you!
We never saw a formal "making" ceremony for anyone in either the novel or the films. In the classical, popular impression of the Mafia, someone is formally "made" in a ceremony that has the Don blessing the new inductee, with a burning saint's card, pricking of the finger with a knife, swearing an oath, etc. And, prior to the "making" ceremony, the new "made man" presumably had to kill someone on orders of the Don or another higher-up.
None of that applied in the novel or the films, except one aspect: Rocco killed Paulie early on, and (in the novel and in a deleted scene from GF), Clemenza flat-out told him, "You
make your bones on Paulie today." I put the emphasis on "make your bones" because that's the only indication that Rocco was thereafter a truly "made man."
The first time we see Neri in the film, he's donning (no pun intended
) a police uniform to assassinate Barzini and his hangers-on. Presumably that's his rite of passage as a made man. In the novel, Neri is carefully recruited and brought along by Clemenza.
SPOILER: When he's been tested, he's dispatched to California to assassinate Moe Green. After that, Michael greets him warmly, and gives him a "living" off of a particularly rich "book" on the east side of Manhattan--as sure an indication that he's "made" as anything else. The novel also says that he took command of the Barzini family after he killed Barzini, though (as you point out) he was later made head of security for the family hotels in Nevada. That seems like a let-down, but, he stayed with Michael, whereas (in the novel) Rocco stayed in New York with Clemenza. So, I'd say that, from the novel's perspective, Neri came out ahead by being close to Michael, whereas Rocco was out of the running.