RFCs and ADRs are great as historical records, but without any documentation of the architecture as-is, this is equivalent to having a blockchain without any state. It makes it difficult for developers to reason about how things currently look, especially for a project with a pretty long-running history.

My recommendation here is to, on each major release branch, maintain at least some documentation for app/consensus engine developers that describes the architecture as-is (i.e. as it is on that particular release branch). This could, for instance, reference specific ADRs, and could also include descriptions of the various components making up the system, as well as descriptions of the different interfaces of the system.