There's currently an ongoing discussion on one of the german SR boards regarding the treatment of armor on cyberlimbs.
It's leading nowhere, as there simply is no definite ruling possible via the game rules and apparently it has never been errata'd or put in the FAQ.
One prominent position is: simply add it over all cyberlimbs (i.e. and up with something like +20 armor if fully cybered).
Arguments for that:
- there is no rule prohibiting it
- it's always been done that way
The other position is to either treat it like worn armor (i.e. highest +armor over all limbs counts) or average over all limbs, like it's done with physical stats
Arguments for that:
- since there is no rule, analogouos rules should be used
- the one rule regarding CL armor says: 'it is cumulative with worn armor', specifically it does not say 'it is cumulative with each other and worn armor'
- other sources of +armor would be completely negated. A lower leg replacement with +3 armor would not only be completely legal, but cost about half the nuyen and essence as orthoskin (with bioware typically being more essence conservating than cyberware) AND also have the possibility of being taken twice