Hi Steve.
If you ave Customer + Product then its straight.
As complete VAS can be executed with packing specification and you can control activity accordingly.
Get the customer and mat combination with VAS activity then create packing spec group with a
PS Group 3>>VAS activities VAS A + VAS B in work center 1
PS Group 3>> VAS activity VAS C in work center 2.
PS Group 3>> VAS activities VAS A + VAS B + VAS C
and then create packing spec accordingly and maintain condition record and check system wil create only those step you want per mat with WC.
I hope this is clear now. you can have any que further if not clear. and like if its resolve ur issue.
Regards
Suraj