I have checked the exact answer boxes, and have listed USA, Virginia, Cumberland County as exact matches. I get every occurrence of Cumberland and West VA is also included.
I am not sure how you are searching. When I go to the Search tab, I click on Records, then on the lower left side I click on "Browse All Published Collections." Then at the top under Filter by Collection Title, I type in United States Census. The Censuses are listed by dates. When you click on the date you are looking for, you will get a page where you can input your ancestors data. If you want to see the complete census records you click on "Browse through ---- images." That will take you a page where the states are listed. Then go to Virginia, then Cumberland County. There may be communities listed above. You can click on the Community you are searching and see the census record with the indexed record below. I hope this helps you in searching the census records.
There is an excellent instruction article in the Research Wiki that might give you additional help.
That was my standard practice. I can get to the census records by date easily enough. BUT, from 1870 onward, despite limiting the search to Virginia, the results invariably have West By-God Virginia included, along with any mention anywhere that has Cumberland which is the VA County to which I need the results restricted. The Exact Terms Only button does not work.
When I did the search for 1880 census, I clicked on "Browse through 1,080,487 images," then on Virginia, then on Cumberland. It gave me the choice of three townships:
There was no West Virginia involved. Am I not understanding the question? It might be easier to understand by phone than by community. You could go to the Contact Us in the help menu to get a phone number to call.