A possible solution would be to add a large penalty term to your loss function based on this constraint. While this does not guarantee that the predictions will satisfy the constraint over many training iteration fewer predictions will break it as the loss is minimized.
Relevant-Number7428 t1_iv9mtl5 wrote
Reply to [D] Enforcing object order in object detection by give_me_the_truth
A possible solution would be to add a large penalty term to your loss function based on this constraint. While this does not guarantee that the predictions will satisfy the constraint over many training iteration fewer predictions will break it as the loss is minimized.