Chances are the threads are knackered.
However, as it has probably to be repaired anyway at some expense, why not give it another go? Trouble is, you can never be sure exactly when the thread takes, up so comparing turns with another plug may not be a reliable yardstick. I suggest giving it a bit more than the three quarter extra turn just in case its a tight spot that may eventually come right with a couple more turns or it will strip the thread properly. Nothing lost. This might be described as a Sh*t or bust approach but has a slim chance you may succeed.
