And there's no requirement for an instructor's endorsement to take the ATP written. It's one of those you have to read between the lines things. There is a requirement for an instructor's sign off for the rec, private and commercial writtens listed in 61.96, .103 and .123 respectively. However in 61.153, the requirements for the ATP, the FAA left that part out. You don't even need a sign off for the checkride unless you fail the first time or you are getting a type rating. It was explained to me that by the time you get to the ATP level, you should know if you are ready for the written and checkride.