Clearly you are obviously more privy to IE board meetings and decisions taken at them than the rest of us.
Might it not cross your mind that they actually may have only formally made the decision not to go ahead with the new timetable at or around the time that they told the public?
While it might have been apparent that the unions were not going to co-operate for some time, it certainly was not obvious that the company were not going to try and force it through. That would have been a board decision.
You're also only looking at external timetables - perhaps NIR had already agreed the new timetables internally and issued new working timetables etc.?
Things are never as black and white in the real world as you seem to think.
The issue here is not really the DART schedule but more so the 10 April deadline which became obsolete as soon as IE announced the cancellation of the 10 minute service. There was no obligation to ram a half baked timetable through even if one side had agreed or not. Services could of remained as normal and no changes were required bar removal of the relief morning service and Newary-Bary now Connolly moving to ICR.
But no they went messing with the timetable, did NIR introduce a network wide schedule on 10 April if not the existing schedule could be operating perfectly normal.
Your are totally correct, things are not as clear cut however with IE they it up a level and we see it timetable after timetable.