I agree with your point about the Heculaneum, but my understanding is we're far enough with research into the form of the Quipus to know that they aren't simply either a linear script or merely accounting data.

For a long time, it was thought that they indeed contained only the latter, but my certainly non-specialist grasp on the matter is that we now know they were used to encode much more than that. In addition to being used directly to verify calculations [0], they contained "histories, laws and ceremonies, and economic accounts" or, as the Spanish testified at the time: "[W]hatever books can tell of histories and laws and ceremonies and accounts of business is all supplied by the quipus so accurately that the result is astonishing"[1]. My---again crude---understanding is this was through embedding categories, names and relational data in addition to numbers, signaled not least through texture and color [2].

I likely come across as if I'm trying to over-inflate the Incan knots, but really it's just to say they appear to be a rather fascinating in-between of legal-administrative inscriptions, whose discovery transformed understanding of Roman institutions over the last century or so, and the straight-forward manuscripts of the Herculaneum.

[0] My elementary and probably out-of-date recollection: an emissary would come to towns with Quipus containing work orders, which would be validated with the community on the spot.

[1] https://www.jstor.org/stable/27087183

[2] https://read.dukeupress.edu/ethnohistory/article-abstract/65..., https://www.jstor.org/stable/483319