question for historians - germanicus and roman names

[caesar44]

hi all of you historians
here is a question with no answer in ancient books
as you know the roman name is divided - private name (publius) , clan name (cornelius) , family name (scipio) and sometimes nickname (africanus)
there were only several private names in rome - gaius , publius , marcus , decimus , manius , sextus , servius , mamercus , lucius , kaeso , geneus/gnaeius , titus , tiberius and maybe 1 or 2 more
in 42 bce there was a roman praetor called tiberius claudius nero , he had 2 sons - tiberius claudius nero (the future emperor) and ... anomaly .. nero claudius drusus where the hell his private name gone ???
drusus's son was the famous germanicus , he to did not have a private name
this is the first time in roman history
so , what was the private name of germanicus (not drusus , not claudius , not nero , not caesar and certainly not germanicus !!!)

[Carinus]

Germanicus was given the name Nero Claudius Drusus at birth, the same as his father. The honorific "Germanicus" was added at his father's death to commemorate the father's victories in Germany.

They were a branch of the Claudii family, thus Germanicus's private name was Nero.

Carinus

[caesar44]

but nero was a family name for centuries , as i explained
nero was not a private name , there were no nero's before drusus as a private name
the claudii nerones were only a tiberius or appius , check it in the books

[Spetulhu]

Might the guy be adopted? IIRC the names were shuffled about a bit if you were adopted.

Perhaps the private name wasn't written down? If someone is famous enough his contemporaries don't need all his names, they know who you're talking about anyway.

Or the records have been damaged? It's been a few centuries since.

[Carinus]

No, he wasn't adopted. What's the problem? Just think Nero Wolfe.

Carinus

[Epistolary Richard]

My knowledge is very rusty, but what's wrong with Drusus as a private name?

As for Germanicus, I thought we didn't know what his real name was, I thought Tactius and Suetonius always referred to him by the honorific.