Look at the definition of "after the fact" - 'occurring, done, or made after something has happened.'
I understand the phrase perfectly, thanks. The suggestion here is they are introducing a course after the deadline for implementation. So in this case, the implementation deadline is the fact the training is coming after.
It's a nonsense to suggest that GDPR 'has happened' as it involves continuing responsibilities.
I don't think anyone here has suggested it has happened and that's the end of it.