There are really 2 different GCVR to look at.
In my case, Ford gives a maximum GCWR of 30,500 pounds. That's the absolute most the truck and trailer can weigh together.
Theoretically, I could have a trailer with a GVWR of 16,500 pounds before maxing out the truck.
The actual GCVR is the total of the GVWRs of the truck and the trailer. For me it's 14,000 for the truck and 11,952 for the trailer for a GCVR on my rig of 25,952 pounds. That's the most the rig can weigh if both truck and trailer are loaded to their legal limits.
That number comes in to play for me here in PA since my class C drivers license limits me to 26,000 pounds. I'm also required to register the truck for the maximum combined weight it will pull.
Confusing? you bet! I just spent a great deal of time figuring all this out with lots of phone calls back and forth with AAA and PennDot.
As always, your millage may vary!!