It has been reported that the SS-21 has four types of conventional warhead; unitary HE fragmentation, anti-runway, anti-armour and anti-personnel submunitions, with 50 anti-armour or anti-personnel munitions carried in each warhead. Following the Intermediate-range Nuclear Forces (INF) Treaty photographs of the SS-23, it would seem quite possible that the SS-21 also has an earth penetration HE...
Odd but I thought unguided rockets got classed like the old FROG designations.