I've seen recently that a few VDL Template users have tried to "update" older scores by importing newer versions of the VDL Template's House Style(s) into them. Let me see if I can explain why this is NOT a recommended procedure.
When Sibelius imports the instrument definitions into a file, it will look at the noteheads lists of both files (House Styles) and compare them. If it sees differences between the lists, it will compensate for the discrepancies by creating new noteheads and adding them to the end of the list. One of the potential side effects of this is corrupted instrument mappings. And once that happens, you can definitely start to see and/or hear errant behavior during input and/or playback.
"So what do we do with older scores we want to update?"
Good question. I'll let Joe Keefe answer that by giving you some things to consider in
this great post. (Excellent info, Joe, thanks!)
If you have scores that are now not functioning the way they did originally (and since all situations will not be the same), start a new forum topic, do your best to explain the specifics, and we'll see if we can't get you fixed up. (Remember, screen shots really help a ton - like the one I've attached here.)
Late
Hugh