Turn and slip,
I am not sure that you have got the important bit about the definition and shoey's comment. The only people who can state categorically that a loss of separation is an AIRPROX are the pilots or controllers invovled in the incident. The replays and investigations can say what happened, why it happened and how it happened BUT it cannot say that the pilot should have reported the incident as an AIRPROX because in the investigator's opinion it was - the defintion is specific in that it is only the pilot or controller at the time of the incident who can say that.
There are numerous instances in aviation, and other industries, where an incident in one circumstance is not considered unsafe but may have been considered completely differently in other circumstances (e.g occurance in VMC, same occurance in IMC - in one the pilots were always visual with the other aircraft - no incident , in the other they were never visual - incident.)