Tempdb with Multiple mdf and Renaming
SQL Server uses a round robin with proportional fill algorithm for TempDB and data files in general.  Thus if you have 1 TempDB file and add 2 more, only the other 2 will be filled until they reach the size of the first one and all will then grow proportionally; or when the next restart occurs and they all get emptied out.  

Thus you will be using those files.  You can see them being used in the physical index stats DMV.  Naming doesn't matter, just do what works for you to manage them.