The policy I'm following in California is that, since the whole point of a business route (per the statute authorizing Caltrans to designate them) it to direct freeway travelers to businesses on the old route it bypassed, once BL signage completely disappears from the mainline, the route is effectively decommissioned, even if there is some -- or a lot -- of residual signage on the locally-maintained business route. In New Mexico, we offed I-40BL Abuquerque, even though there was one stray old BL marker left along that fairly long former route.
Maybe in Ohio the state maintains those BLs, and/or has a current official list of business routes, so the state hasn't officially de-designated them, and since they have some route signage we can't treat them as unsigned routes.