Controllers shall aim to pass information on relevant traffic before the conflicting aircraft is within 5 NM
Key word here being relevant - under RIS anything that would penetrate a 5nm bubble would be called regardless of whether it was relevant or not eg passing behind. I agree with the problems of service creep but also I couldn't sleep at night if I had a chance to highlight a possible confliction and didn't and the worse happened... If the blips will merge and one is unknown (non-squawking or no mode C) I will always provide at least a generic traffic warning or a reminder to keep your eyes peeled...