You can take into account the deployment stack of players with a turn order before yourself. So, for example, if you are the second player in turn order, you are only permitted to get information about the first player's deployment stack, not the third or fourth.
You are allowed to wait until players before you lock in their deployment stacks, before locking your own in. You are permitted to know which units those players are deploying and in what order. You can also know what units are being grouped together and the order of those units.