If you're going to offer different preorder bonus content through different retailers, announce all of those offers simultaneously... or at least inform us that further offers are upcoming. Otherwise, you're ensuring that some customers will have to cancel one preorder to place another so they get the specific bonus content they want.
A choice is less of a choice if not all options are on the table when the decision is made.
If physicians take an oath to do no harm, salesman can at least try to avoid needlessly annoying their customers.
I'm looking at you, Warner Brothers.