Each OMS (order management system) in an OMS chain  remembers the state of each order . Let’s focus on OMS4. When OMS4 receives an order-cancel/replace request message from upstream, will OMS4 accept the request and send the message downstream? Depends on the order state (of the order8) in question.
I believe if the order has been already rejected or fully filled or cancelled then not possible. OMS4 would reject the request.
What if order8 is in New state? That means acknowledged by liquidity venue but no fill received yet. Yes request is acceptable.
What if order8 is in PendingNew? That means OMS4 has not received the acknowledgement from downstream. meaning the liquidity venue has yet to enqueue the order. Well, in this case cancel (or replace) request will be forwarded to liquidity venue. OMS4 can optionally send back a PendingCancel or PendingReplace to indicate the current order status. In time, liquidity venue will either accept the request, or reject it because “already filled”, and send this response to OMS4.
 in non-volatile memory, and can respond to status queries and can often broadcast the order status to subscribers.
 A large trading platform often has a chain consisting of multiple OMS nodes, such as clientConnectivity, smartOrderRouter, AlgoEngine. I feel should not be more than 5 nodes, unless some aggregation is required.