Here is the relevant portion of rule R11, for reference:
Robots may use either:
Option 1: Up to ten (10) VEX EDR motors or VEX Servos (Any combination, up to ten) and a legal VRC pneumatic system. (See )
Option 2: Up to twelve (12) VEX EDR motors or VEX Servos (Any combination, up to twelve) and no pneumatic components, excluding pneumatic tubing.
And rule R18:
Pneumatic devices may only be charged to a maximum of 100 psi. Teams may only use a maximum of two (2) legal VEX pneumatic air reservoirs on a Robot.
If using Option 1, there is no limit to the number of pneumatic cylinders that can be used on a robot. The cylinders are not added to the total number of servos and motors. The only restrictions to be considered a "legal pneumatic system" are found in rule R18, quoted above.
@Elisabeth_H It is also unclear as to what counts as a pneumatic system
For the purposes of rule R11, a "pneumatic system" is considered any set of pneumatic components that does not violate rule R18. That is, as soon as any pneumatic components are added to the robot (excluding pneumatic tubing), a robot is no longer eligible for Option 2, and is thus restricted to ten (10) motors or servos.