These are conditional offers that we send based on gaps left by trainees who will potentially move after the first iteration of offers, to fill those potential gaps.
When we send anonymous information on eligible trainees to training regions, we also send them an anonymous list of all the trainees that have applied to leave their region. This is so they can let us know, if that trainee receives a conditional offer, that they wish to fill that potential gap with another IDT.
If you receive a second iteration offer, it simply means that we were able to offer you a post because someone is leaving the training region on an IDT that you want to join. Your ability to move may well be dependent on the trainee leaving your potential gap.