Numbers like that refer to the type and arrangement of accomodations of the sleeper.
A 10-6 is 10 roomettes and 6 double bedrooms.
A 4-4-2 is 4 bedrooms, 4 compartments, and 2 drawing rooms.
A 6-5-2 is 6 roomettes, 5 double bedrooms, and 2 compartments.
Somewhere there is or ought to be a complete breakdown chart, but I can't think of where.
Ed