The OPC server only contains whatever is the most recent data. It doesn't store any history. So depending on how quickly you update the server and how quickly you read it, will determine what data you get.
If you update it with Data1, Data2, Data3, Data4, Data5, 5 times per second, but only read the server at 1 time per second. You are only going to get one of those values.
If you update the server once per second with Data1, but read it 5 times per second, then you are going to get Data1, Data1, Data1, Data1, Data1.
Explain what you are trying to do in your application. If you are concerned about losing data, then using a OPC server is probably not the right solution for you. It is like the difference between reading local variables in LabVIEW to pass data between loops versus using a queue to pass data.
