All you have to do is register your ITSSAR qualification with RTITB who will then add it to your remit. A CPD should make registering it on NORS ok. If in doubt speak to Nick Welch at RTITB.
As RTITB & ITSSAR are both members of the ABA2012 Workplace Transport it should be ok as they recognise each others qualifications. As for the ITSSAR standard allowing shortened courses this is not true. The only way ITSSAR & RTITB allow the shortening of a course is on in house training only where the training day can be reduced by upto a maximum of one hour per day - this is the case for both awarding bodies