Did you read the help? It's usually helpful.
Based on what I read, it would appear that for third party add-ins the Command parameter will always be swCommands_e.swCommands_User_Toolbar_Min
It appears to describe the method by which CommandIDs are assigned. As far as I can tell from the help file, the CommandID is an integer specified by the creating application at the time of the toolbar item creation. Therefore, it seems somewhat unlikely that the third-party app would assign different CommandID numbers for different users, but it is certainly possible, and entirely within the control of the third-party add-in. You would have to confirm that with the third-party vendor.
You might also be confused: The Help file is actually a bit hosed. Parameter section for CommandOpenPreNotify references and links to swCommand_e. However, it should actually link to swCommands_e.
Also, the list in swCommands_e is hosed. User_Toolbar_Min is not shown in the list, and User_Toolbar_Max description is wrong.
I have provided feedback to the Help folks on both of these issues.
I know that the help is helpful and it is always my first source of information.
On this subject the help text was a little cryptic to me, so I am glad that you explained it to me in layman terms.
Thank you for that!