Playing as the Refuge on the Immense setting and I got four lucky rangers in about 6 or 7 turns. I think that either I am TRULY lucky or there is a probability counter a little off somewhere. I can post the game is you want.  This happened fairly late in the game so I'm not sure if its a catch up feature or if something actually was broken.  Around the same time a bunch of other civs found corvettes.  I as well got a corvette too so I don't know what to make of it.