This morning for a few hours I was monitoring 123.925 and 135.575, and watching the traffic using Flight Explorer. At that time (around 09:00am EDT) they were using 123.925 for CVG departures flying the CINCINNATI-9 SID via RIKLE or DQN, and using 135.575 for CVG departures flying the ROCKT-1 and JODUB-2 SIDs.
The latest Indianapolis sector map I have does not show the 135.575 sector, although from the older chart I have and from monitoring, it appears 135.575 overlays part of the York (134.000) and River (124.225) sectors that include the ROCKT and JODUB SID routings, FL230 and below.
Also noted on 135.575 were CMH departures southbound via J186 to ATL and TPA, checking on climbing out of 7000-8000 for 10000, then cleared to FL230 before handoff to the high sector.
Maybe those EWR departures were re-routed off their normal route via RIKLE over to ROCKT or JODUB due weather or traffic ? Or maybe 135.575 is only used during peak times and they split the sectors depending on traffic volume ? I know, doesn't really answer your question. I'm kinda busy over the next week, but maybe the following week I can take a closer look at these sectors and routes out of CVG.