Question about 'Presentation of Radar information'
 

When I read the part 'radar services' in doc4444, concerning about 'Presentation of Radar information', it says 'When applicable, distinct symbols should be used for presentation of:
a) unintentionally duplicated SSR codes;
b) predicted positions for a non-updated track; and
c) plot and track data.
I can't understand a,b and c above, could anybody make some detailed explaination about that or take some examples if possible.
I would really appreaciate it. Thanks a lot.