It looks like that you requirements are a bit different from what the OPC specs prescribe. So yes, you can still do that, but with additional processing on your side, as you suggested.

Best regards

Hello.
there are no such terms defined in the OPC spec.

I suppose that when they say they say "polled" mean, they mean the usage of OPC Read calls. That corresponds to IEasyDAClient.ReadXXXX methods.
And when they say "Exception", they mean the OPC subscription mechanism, which corresponds to the usage of EasyDAClient.SubscribeXXXX methods.

But I think that their answer actual does not relate to your question. My understanding is that you are already using subscriptions.

Regards

Hello.

it is incorrect to think of the subscription mechanism as if the library of actively acquiring anything. The subscriptions in EasyDAClient rely on the underlying OPC subscriptions, and the EasyDAClient simply send you whatever the OPC server sends to the EasyDAClient.

So, if you have concerns about how it works, you should look for answers in the OPC specifications and on the server side, but not on the client side.
In general, servers should be sending the updates in the time order.

The library instructs the server to provide the subscription updates, and then it simply "waits" until the server provides something, and it sends it to you - in the same order as it was received from the server. It does not change the order, it does not change the values, it does not change the timestamps, it does not change the qualities, it does not filter anything out. That is by design.

Some servers do not send out notifications if the value has not changed. But some will happily send out a notification with the same value, if they have acquired a new data and the timestamp has changed. OPC "Classic" is not quite consistent in that. OPC UA has it defined somewhat better.

Regards