I'm going to try and follow this:
Just because words and meaning don't derive from specific or identifiable individuals doesn't mean they don't emerge materially.
There is ink on a specially processed thin layer of wood or other substances. The form the ink takes is abstract and immaterial.
Immaterial was a poor word choice but atm I do not have something more appropriate. These letters, their shape and arrangement to include syntax, don't have any sort of inherent properties, rules, etc. It is all completely arbitrary and abstract. There is nothing inherently "A-ish" about the letter A. I'm not sure if that is sufficient to explain what I am calling into question regarding their "materialness".
The materiality of the signifier is entirely contingent; the fact that signifiers assume the form they do is not in accord with some predetermined essence. I'm not sure why you think I'm suggesting that's not the case, or how anything I've said contradicts this.
Language, in this material sense, is not "created" by any single individual, nor can its "creation" be quantified among multiple individuals. The entire process of language production is an unconscious, collective effort that would not have even found the need for existence among only one individual.
There was no first person to use a signifier; the use of any signifier, for the very reason it comes into existence, is predicated upon an acknowledgement that its use is communal and is only effective if one person is not the only individual meaning it (or making it "mean"). There can only have been the first group of people to use a signifier, and the individuality of these people, while biologically true, cannot be ascertained from their participation in the use of a signifier.
Your approach suggests that a message can, theoretically, be quantified and its pieces be parceled out among the group, thus committing each portion to the proper individual who meant it. This, however, is not even the case theoretically; meaning cannot be traced back to parties in this way. Individuals only mean something based on what prior rules/norms have been established by the group. Meaning is never entirely individual; it is always collective.
I'm not denying that individual sensations and emotions taking place within the body aren't individual; but the linguistic process is not individual, and by taking part in language a subject assumes the role in an institution that is determined collectively. In "How Words Do Things With Us," Dennett writes:
The back-and-forth process that narrows the distance is a feedback process of sorts, but it is just as possible for the content-to-be-expressed to be adjusted in the direction of some candidate expression, as for the candidate expression to be replaced or edited so better to accommodate the content-to-be-expressed. In this way, the most accessible or available words and phrases could actually change the content of the experience
What Dennett suggests is that individuals certainly experience sensations that aren't felt collectively; but their expression is determined by collective terms, by linguistic processes that are not the result of solely individual creation or decision. The group decides the best signifiers to use, and unconsciously conditions its members to navigate language based on the assumption that it is a collective institution.