The new Gearboxes and the old gear boxes do NOT use the same gear for the CIM Motor. They are just different enough that are NOT interchangeable. Make sure to keep the extra gear from this years box, and the extras from old gear boxes separated.The new kit bot uses dual stage mini toughboxs with 12.75:1 gear ratio(in 14t, lg cluster 50t, sm cluster 14t, out 50t) instead of 4.67:1(in 12t, out 56t) in the old single stage CIMple box. The extra pinion gears in the KOP are in case you want to add a 2nd motor to the new gearboxes. They are not intended to be used in the CIMple box.
Good to know.
BTW, CIM, not SIM.
If you order from VexPro, you can get 2 different sizes, but 4 different tooth counts. http://www.vexrobotics.com/cim-motor-gears.html