Whether you can still apply for this cycle or not depends on your reasoning for a late application that you would present to the Atlantic Bridge Program, IMO.
This time of year is when applicants find out their interview decisions and/or receive the last of their interview invites. Therefore, a lot of students would be applying now to Irish medical schools as a fallback. Putting Irish medical schools into plan B and sending a late application to the ABP will not help you. You're also competing against Canadians with better stats. Usually, Americans go DO or to the Caribbean before going to Ireland.
Anyhow, I snuck a screenshot of one of my allopathic interview invitations into my first contacts with the ABP in September prior to my application submission (before the deadline) assuming what I described, above. I'm an American, too. The more you read this forum, the more you'll see that its mostly Canadians going to Ireland. Good luck.