There were a total of 15,264,063 votes cast in elections in Virginia in the time frame you reference (May 2011 to May 2017).

http://www.elections.virginia.gov/resultsreports/registration-statistics/registrationturnout-statistics/

So, what percentage of the total vote did those 7,474 illegal ballots constitute?  About 0.049%.

Not very indicative of a problem that would allow HRC to win by 3 million votes...never mind that you're assuming that all ballots cast illegally would always go the same way, as I showed with my example in Kansas.