I am going to muddy up this discussion but, hopefully clear up something too. The NEC does not have much in the way of codes for storable pools and in some instances goes out of its way to avoid the discussion on them. However, it does speak to this very topic in article 680.7 (A).
680.7 Cord-and-Plug-Connected Equipment. Fixed or stationary equipment other than an underwater luminaire for permanently installed pools, storable pools, outdoor spas, outdoor hot tubs, or fountains can be cord-and-plug-connected to facilitate removal or disconnection for maintenance or repair.
(A) Length. Except for storable pools, the cord must not exceed 3 ft.
The NEC does not specify a maximum length for storable pools. It does not allow for extension cords to be used but a properly fitted longer cord of the proper outdoor rated material can be fitted. Again the water gets a little murky if the pump is UL listed with the cord it came with and it is replaced with a longer one.