The story of pinks mammoth is quite a tale and I have told it before. It is probably the oldest, biggest and is certainly one of the best atemoyas if not Annonas. From memory the recollections of a Brisbane botanic gardens worker of a fabulous human head sized fruit encountered in the 1860s in Suriname, French Guiana or somewhere around there cause a hunt. They were located and brought to Australia in the 1890s.Their story of survival and blossoming into the standard by which all others were judged for 100 years is quite a tale. All serious breeding programs in Australia try to impart or retain the mammoth taste.
Ok I am just a bit too warm, for quality fruit and I think Puerto Vallarta is also a little too warm to grow mammoth atemoya with winter minimum temps ideally around 8c to 13c on average and getting down to around 3c to 5c. I think you are more like 15c to 17c on average and rarely getting down to 10c. Rainfall of around 1400mm/yr is good. From seed they go well and stabilised a long time ago with numerous seedling generations. Hillary white and paxton prolific are bud sports so who know what would grow out of those.