I am glad you asked this question, because it shows a misunderstanding that needs to be clarified. It is not your fault, though - we probably need to make it much clearer in the documentation.
I think the misunderstanding comes from the term "RTD Server" (which is not something we have made up; it is an official term from Microsoft). This is not a "server" in a sense of something like SQL Server or OPC Server. It is, basically, a local COM component - a piece of code compiled and linked to an EXE or DLL - that exposes certain functionality to Excel and integrates into its "RTD" function in Excel formulas. In case of QuickOPC Excel Option, this RTD Server equals to the set of QuickOPC assemblies (DLLs), that need to be placed on the machine where the Excel process runs, and registered with COM (using RegAsm utility).
So, if you intend to use the QuickOPC Excel Option to connect from Excel to OPC servers, and there will be multiple computers running the Excel, each of them will have its own "RTD Server" installed (the QuickOPC assemblies). And each of them will connect from Excel through its own RTD server to the target OPC servers (which can then be on different computers as well). There will be no central RTD Server.
The QuickOPC licensing then reflects this. QuickOPC license is physically located in the rgistry at the machine where QuickOPC runs. In this case, QuickOPC (exposing its RTD server component) will tun on each computer where the users run Excel, and that's where the license needs to be installed. When not installed, that particular computer will fall back to using the 30-minute trial license (counted from each start of the process hosting the QuickOPC, which would be the Excel application in this case).
Note: Actually, at least theoretically, it would be possible to deploy the RTD server centrally, and then specify its location in the Excel RTD function. It may work, we do not support this scenario, and have not even ever tested it. In this case, Excel would need to to connect to the remote RTD server using DCOM, and that would bring all the DCOM headaches with it (configuration, security, performance). So forget that for future considerations; I just wanted this discussion to be technically complete.
