Am not very clued into the way Asia Miles works and so was wondering whats the time-limit for logging in flights into one's Asia Miles account..??

My mum completed some long-haul flights on CX earlier this year & i was under the impression that she was a member on the program already. Found out she was not and bout a month or so after her flight, signed her up and tried updating the completed flights and kept getting a message saying the time-limit had lapsed and it's not possible..