Non creditIng may not always be due to "incompetence of staff". If the FFP is keyed in properly it should show on the boarding pass; even so I've had trips where this was done properly by checkin staff and shown on BP, but still miles weren't credited automatically and I had to initiate manual reclaim. Annoying when that happens but it could be due to breakdown of data that passes from one airline to another (in your case AI to SQ).