Had Virginia ratified the amendment prior to December 1816 then they would have been the 13th state to do so and the necessary 2/3rds would have been reached. But in March 1819 there were 21 states. Virginia’s ratification meant nothing unless 2 more states ratified it as well. They didn’t. Bingo, this is much more clear and concise than what I said. The original 13th failed to mee the requrements at the time the last state ratified.