Hello Andreas,
the probable attacks were the ones Supermarina considered sound, i.e. ASW actions where there was a solid chance there was really a submarine. Without this appreciation it was only a contact or a sighting and even if depth charches had been dropped no enemy sub was actually present.
There were 194 probable attacks between 13 June 1940 and 20 Aug. 1943.
However, even if this action is not incuded in that record the same book says, pages 179 - 180, that on 7 Jan. 1942 orsa was escorting the motorship Probitas off the Kerkenah is., had a sonar contact, attacked twice dropping a tital of 19 depth charges, observed naptha and wooden debrits and appreciated to have damaged an enemy boat. Supermarina had the same opinion. According British sources only Urge and Upright were in that same area and that Upright had to leave her patrol on 9 Jan. 1942 and to come back to Malta for lacking in the battery room. As nothing is known about the origin of this defects the attack was not included, after the war, in the a.m. 194 ones.
Greetings
Enrico