All factory evaps on 850s (only) have white plastic rings that are loosely positioned on each of the two evap pipes where they attach to the AC lines at the firewall. You will ONLY see these on cars with original evaps as it's a leftover from the factory install. Those rings are not used on the replacement evaps so when it's replaced, they fall on the floor usually and never seen again. So, if you're looking at that area by the firewall where the evap connects to the other lines and don't see those white rings, then you'll know that the car has had (at least) one replacement evap. Also look for AC dye stickers under the hood as that means that at one time there was a leak and dye was added with a recharge to locate the source.