Some uses of plural are not collective at all, or rather in them, the collective aspect is secondary.
The majesty "we" was used by queens and kings, but also by other people with official roles (up to being ridiculous). The editorial "we" may be considered a similar case, with the author of a newspaper article speaking in the name of the editorial board.
A compassion "we" is being reported, used by doctors with their patients, but also mothers with their child, and maybe by teachers with their pupils. This use builds up an association.
There is finally the modesty "we", used by a scientist to signal the author's not claiming ownership of the expressed ideas or observations.
Our "we" is indeed collective, but not universal --most people do not share our concerns, experiences or opinions. It is neither bounded nor global: anybody is free to adhere to it. Like the compassion "we", it is projective, but like the modesty "we", it is contractual: you are free to refute belonging to it -- you are then compelled to position yourself. Finally, it is contextual: different "we" bindings are not always related to each other.
There is a sense of objective scientificity in it: "we" is a defeasible theory (see Karl Popper).