The yellow card just identifies you as a connecting passenger, so that downstream airport staff can direct you to the Connections CBSA booths. But, as discussed a bit upthread, YVR has no OSS, nor will it for a long time without renovations. If you have Nexus, there's no point to the connections process in YVR. We skip it, use Nexus, exit with YVR-destined passengers and go back in to domestic from the "Outside".

Of course, we never have checked baggage, so I'm not sure if that is a problem if you have checked baggage and don't go through the Connections hallway.