Currently, the ILLHiddenRequestStatuses sys preference reads: "... The request codes can be found in the ILLSTATUS authorized value category." But, the request status codes actually come from status_graph of their respective backend, or alternatively from core Koha::Illrequest, not from ILLSTATUS. ILLSTATUS AV is only used for a request's status_alias, which is an alternate list of statuses that is only used to give the staff member the ability of adding their own statuses by editing a request. On top of that, bug 28641 refers to the fact that the code that is checking this system preference doesn't even consider the requests' status_alias, only the actual status coming status_graph in code. I think this label should be updated to reflect that it may use both the status codes from installed ILL backends and the values from ILLSTATUS, once 28641 is fixed.
That certainly makes sense. If we changed the description we could also update Bug 28641 - ILLHiddenRequestStatuses does not consider custom statuses to be an enhancement instead of a bug.
I think if we push bug 28641 and bug 32799, this will no longer be needed.
+1
Closing this as the problem described has been fixed by bug 28641 and 32799 and both have been pushed.