The Amazon MWS Reports API has an Acknowledged parameter available for returning all outstanding orders that have not been previously acknowledged by the merchant.
So far I haven't been able to find an equivalent parameter that I can use with the MWS Orders API, so I have to work my way through the past 30 days worth of orders using the ListOrdersByNextToken call(s), which come with a fairly severe (and apparently incorrectly documented) call threshold and refresh limit. I'm really hoping I've missed something in the documentation and/or the schemas about acknowledged vs. unacknowledged orders with the Orders API. If this is the case I'd certainly appreciate it if anyone could point me in the right direction.
Right now I'm leaning towards trying the LastUpdatedAfterparameter instead of the CreatedAfter parameter, but I'm absolutely certain the former will always retrieve all new and unshipped orders from the Amazon Marketplace.
It's possible to acknowledge individual orders by sending Amazon a
_POST_ORDER_ACKNOWLEDGEMENT_DATA_XML feed or a_POST_FLAT_FILE_ORDER_ACKNOWLEDGEMENT_DATA_tab delimited feed however, there's no way (as far as I can tell) to solely pull unacknowledged orders using the Orders API.You can schedule order reports using the Reports API and then pull unacknowledged order reports as you would with other kinds of reports. I think this is probably the closest feature to what you are looking for.