According to Sandy, according to the 1994 Alps catalogue, the SKFR/SKFS series comprises the following:
Two approaches to LEDs were taken. SKFRAD has a short front-to-back depth and leaves room for an external LED, while SKFRFA–C support an internal LED. A switch matching the description of any of SKFRFA–C has yet to be seen in the wild.
SKFSAA is a tactile switch, although the design produces a subtle click.