Hi Paddy, howz OZ? So only a couple of threads showing on placement? - Thats completely normal, so it does indeed sound like progessive failure. This could happen in seemingly sound rock. Even when drilling there is only a vague brief feedback to the drill from which to form a judgement, really hard to tell. I strongly recommend inspecting the inside of the hole and not stopping brushing with a stiff nylon bristled brush until dust stops coming out the hole, this should reveal any definite problems. In this case it sounds like things werent that obvious.
Stu:- Nah just gluing some suspect holds on two routes, one is a big flake that could kill so hope to stabilise it. The only concern with putting a long mechanical in the Paarl rocks route is if the ouside rock fails there will be little to hold in the sleeve? Glue-ins are easy to place, if need help just holla - ltrz.