It looks like there's no way of deciding whether the order was actually modified without placing a req[All]OpenOrders call. I don't usually modify working orders but if I had to approach this problem I would likely use a circular awaitable future structure that would wait for two events to complete together: an OpenOrderEnd callback and an ExecutionEnd callback, and make a new req[All]OpenOrders call every time these two events have happened. In C# structurally this can be done either with regular events or two TaskCompletionSource objects and an await Task.WhenAll (or similar) call in a cycle. Doing this would ensure optimally timed calls to req[All]OpenOrders that would neither overlap each other nor fire needlessly in the absense of new Executions. Overall while this would inevitably lead to quite many req[All]OpenOrders calls, these will actually not require much processing power or connection hopping since these data are already in TWS so getting and processing it through the socket is going to be cheap even with some redundancy, which seems to be inevitable here
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Best,
DS
