While common, a caporegime isn't necessarily in charge of a sub-family or a crew, it can also refer to someone of high rank within a family, from wikipedia...
Caporegime is an Italian word, which is used to signify the head of a
family in Sicily, but has now come to mean a ranking member, similar
to captain or senior sergeant in a military unit.
And this is true of Al Neri...
In The Godfather Part II, Neri is seen to be an unofficial
second-in-command to Michael, and serves as one of Michael's capos
along with Rocco Lampone and Frank Pentangeli. He is responsible for a
prostitute's murder that guarantees the loyalty of Senator Pat Geary.
Neri was also personally responsible for the assassination of
Michael's brother Fredo Corleone, under Michael's orders for Fredo's
After Michael Corleone takes over the family, he makes [Rocco] Lampone a
caporegime. In the book, Michael puts together a secret regime for
Lampone, on the advice of Vito Corleone;
Even if this weren't true, it could also be possible the FBI considered them capos based on their imperfect knowledge of the Corleone family. The government only identified 4 ranks in the family: Boss-Underboss-Capos-Button Men. Neri and Rocco are clearly not button men, so while they might not run crews, they are clearly trusted by Michael and very high-ranking within the family.