There are reasons R’s don’t contest seats, and D’s don’t contest seats. Because they have absolutely no chance of winning.
When a major party doesn’t field a candidate, sometimes a third-party or independent files. In any case, in Virginia, you can write-in a candidate.
The votes for third-party and indy candidates in races without a major party candidate is always much larger than when both major parties are represented. Ditto write-ins. There are few write-ins when both major parties are represented, and a big percentage when only one major party is represented.
There potentially are other votes missing. For example, the drop-off from the Presidential vote. But, this is difficult to estimate in a year when you don’t have a Pres., U.S. Senate or Gov. race. I could maybe jimmy up an estimate as best as possible in the absence of a statewide race, but I don’t have the time.
You are assuming the Republican vote in a Democratic district will equal the average Republican vote in contested races. This is way wrong.
I’m not assuming anything. It’s asinine to include uncontested vote totals in the total popular vote. Even the Washington Post didn’t do it. I’m not disputing that PA, WI and MI are to the right of VA, but whether you like it or not the GOP won the popular vote in the contested races last night and they would have held the HOD under the old maps.