Number is typically something that applies to nouns. In English, determinatives enter into scalar relationship and select singular or plural heads, but does it makes sense from a semantic point of view to say that a determinative like several is plural or that all can be singular or plural? What about something like which or certain? I can find lots on number and nouns, but not on the semantic number of determinatives.
It's really hard to know what you would mean by semantic plural when it comes to things that are not nouns. Given that quantifiers bring plurality into the equation, you could argue that most are plural - every, many, several, pair, etc. You can say that those that pick out individual items like each or only are singular. But you'd end up with a lot of indeterminate cases.
In languages that have agreement between determiners and nouns, the determiners will end up with a plural form. But you get up with all sorts of crazy exceptions. In English, a good example is 'pair' which is semantically plural but you talk about 'a pair of lovers walks in'.
So you're better off just describing the system than worrying about what is ultimately a fundamentally artificial distinction.