that is true i remeber way back that one spy for china tried to steal info about the f 16 engine but he failed and got caught.
having the engine and having the documents to the engine are complety different situations. having the engine firstly china doesnt get to keep the engine but only to examine it for a short while, then you have the process of re-engineering which takes time. on the other hand obtaining documents to the f-16 engine the process of contructing such simular engine time is reduce and so are its cost....F-16 engine tech was already available in Pakistan so that wouldn't have been an issue.