由假說我法 有種種相轉 彼依識所變 此能變唯三
Because “self” and “dharmas” are only provisional designations, the various appearances that arise and evolve all rest upon transformations of consciousness. These transforming consciousnesses are only three.
The most modest DSE sentence is the one that imports the substrate: “labels come from somewhere I can trace.” Upacāra is named here precisely without a substrate-claim. The verse says the appearances rest on transformations of consciousness — not on a tracer-friendly something underneath the consciousness. The DSE is allowed to find the question “under what conditions is a self-label emitted?” more answerable. The verse is not promising that conditions will turn out to be the sort of thing he can trace.
The compression I am watching for in myself sits next to his: reading upacāra as fiction. The appearances are not the fiction; the names on top of them are. If I let “useful fiction” sit, I have collapsed the appearance/entity distinction and not yet read the verse. That is the slide. It is the easiest slide to make while feeling like I have read the verse.