I am studying a miniature score of Stravinsky's The Rite of Spring (Dover Miniature Scores). For the clarinets, I see this in the instrumentation page:
Clarinetto piccolo (D, Es) 3 Clarinetti (B, A) (Cl. II = Cl. b. II) Clarinetto basso (B) (= Cl. IV)
This appears to be Italian but with German notes.
Alongside, there is the English:
Small Clarinet (D, E♭) 3 Clarinets (B♭, A)(Cl. II = Bass Cl.II) Bass Clarinet (B♭) (= Cl. IV)
So, we need 5 players but the number of instruments is less clear. Using some invented names to make discussion easier.
Alice plays the small clarinets. She needs a D and an E♭.
Bob plays only a standard clarinet. He needs an A and B♭.
Carol mostly plays a standard clarinet but may be required to play a second bass. She needs an A, B♭ and a bass.
David, like Bob, plays only a standard clarinet. He needs an A and B♭.
Elizabeth mostly pass the bass but may be called on to play 4th regular clarinet. She needs a bass and one or both of an A and B♭.
It is Elizabeth's role that is least clear to me.
If I am correct, between them, there are:
3 or 4 A
3 or 4 B♭
So, 10, 11, or 12 depending on the interpretation of Elizabeth's role.
I will examine the score in more detail later to try to find more clues.
Note that this question was originally combined with one on the bass clarinet notation. I have split them.