2005 was the first year of the plastic table performer and they have changed very little since then. I have a 2008 and I’m sure a 2014 cover would fit mine just fine.
Prior to 2005 performers were a little smaller, a lot lower and had a SS table.
If you think the grill is older than 2005 and it has a plastic table it might be a platinum, they looked just like performers with the cart and single table to the side. The give away fetcher is platinums did not have propane igniters and performers did.