The US DoT would not have any data on Ryanair. Ryanair are doing what they did with the AUC data - using someone else's numbers, sticking in their own numbers on top and then claiming that that US DoT/AUC/whoever confirmed their figures.
There are REAL on-time figures out there. Ryanair come 12th in data from UK airports. See my previous post for more details (#163, page 9 of this thread).