An A330 Captain expressed concern that holes in the engine cowls had been written up requiring repair within 50 flight hours but when that time was exceeded the restriction was altered to require maintenance at the 'next extended ground time'.

Narrative

When looking at the Aircraft Maintenance Log (AML) at altitude; I noticed a write-up for holes in the left engine [cowling]. My Relief Pilot confirmed that he had seen the holes on his walk around and they had yellow paint. I could not find the paperwork within the logbook on these holes. The logbook page indicated they would be fixed within 50 hours of flying. On this date it was clear from the log book pages the aircraft had flown over 50 hours. I had a similar write up in June with the same 50 hours mentioned. There was paperwork about the damage again mentioning the 50 hours. This time there was a mechanic nearby and when I asked about the 50 hours; he left and returned with new paperwork saying it would be fixed the next 'extended ground time'.If we see the yellow paint; we are not required to check the damage list in the AML. There is something incongruent about the 50 hours for repair; which can be changed to 'extended ground time' when challenged; rewritten up again as a repair in 50 hours; not included in the damage list; and flying the airplane well over 50 hours again. Whatever the procedure is for damage to the engines and repair time; the process is not transparent or consistent. This makes any kind of error trapping by pilots virtually impossible.