Timing is set via shims under the injection pump, therefore unless it breaks a timing gear (near to impossible) it's not out of time, and they just can not slip out of time.
If there is any air in the line between the injection pump and the injector (even one tiny bubble) the injectors will not pop open, they will seep but not spray,and not move fuel, and that spray is needed to make it fire along with a working set of glow plugs.
Bleeding it sometimes takes a lot longer than one would think.
Have you confirmed that the glow plugs are getting power and indeed getting hot?