'Differences training' was deliberately changed to 'conversion training' in REV08, because some ex-CAA barrack room lawyers kept suggesting that
only the specific 'differences training' listed in the ANO could count as 'differences training'...
If, for example, you've flown an RF5B with its retractable monowheel and 3-position prop, then fly a PA28-140 for your SSEA Class Rating training, you cannot then fly as PIC in a PA28-180R (with a VP prop and retractable undercarriage) without completing 'differences' training for VP and RG. Or assume that the tail-dragger configuration of the RF5B will cover you to fly a Chipmunk.
Whoever countersigns the application form for adding an SSEA Class Rating to an NPPL (SLMG) is also declaring that the applicant meets the same NST/GST standards as an ab-initio NPPL SSEA applicant, although there is no formal requirement to fly the tests.
REV08 was approved by the CAA; certain statements made at the FIE/CPL conference were slightly incorrect - LASORS 2010 (if it ever gets published) will, however, hopefully correct these errors.