The scoreboard has space for server_limit parents and server_limit*thread_limit workers, but ap_get_scoreboard_{worker,process} allow indizes 0 ... server_limit and 0 ... thread_limit inclusive, but they only should allow 0 ... server_limit-1 and 0 ... thread_limit-1 If the rest of the code is correct, they probably won't be called with bad arguments, thus this is mostly of code cosmetic interrest.
Created attachment 12673 [details] Patch fixing index checks in ap_get_scoreboard_{worker,process}
Apparently this was fixed some time ago, I just managed to 'unfix it' but I've restored your recommended behavior. Thanks for the submission!