Hi,
a closed loop stepper and driver is between the stepper and driver, not the Arduino.
If the Arduino commands 1000 steps CW for instance the driver issues 1000 pulses to the stepper, plus or minus any pulses necessary for the stepper
to arrive in the right location, the plus or minus steps are at the sole discretion of the.driver/stepper encoder combination.
The best the Arduino can do is assume that the stepper got to its commanded location. If it did not the driver would know that for whatever reason, maybe overload,
that the stepper cannot get to its commanded location the drive will fault 'following error'.
To my knowledge no closed loop stepper drivers have the ability to report the current encoder count to the motion controller to monitor.
Modern AC servos do have that feature however.
Closed loop steppers are still cheaper than entry level AC servos but the price gap is increasingly narrow. Closed loop steppers do have some advantages
over open loop steppers but far FAR less than the manufacturers claim, and to my mind are not worth the premium paid. If you want closed loop 'goodness'
go for AC servos and be done with it.
A modern AC servo will EAT any stepper, open or closed loop, ever made.
Craig