(By Hedvig Skirgård): "This question concerns a bound grammatical marker of dual number on nouns. The marker should occur with an open set of nouns, not with a restricted set. This feature contrasts with GB317 Is dual number regularly marked in the noun phrase by a phonologically free element? which focuses on the non-bound marking of dual number. For more on bound marking, please see this page. Bound marking of number on nouns derived from other word classes (such as adjectives or verbs) does not suffice for a 1. ❡
Number marking is often fused with marking of other categories, such as definiteness/specificity or gender/noun class. It is possible for the number marker to also signal other functions and be coded as 1, as long as these other functions do not interfere with the number distinctions and as long as number marking is productive and regular. ❡
It can be difficult to determine how obligatory markers of dual, trial and paucal number are since they can often be replaced by plural number marking. If the grammar writer describes the marker as denoting grammatical number and there are several examples, this suffices."
By "a bound grammatical marker of dual number", the feature description probably means a dual affix (because dual clitics are described rarely if ever, and dual marking by endophony seems to be negligible as well). Dual number markers can be distinguished from numerals ('two') by their boundness (not obligatoriness), as numerals can always occur on their own in elliptical contexts.