Keeeeeeeeeeeriste, I'll get this in before the lock . . .
Comparative dates on which the Nationals notched their 20th win, each season:
2017 - 5th May (29th match)
2016 - 9th May (32d match of season)
2013 - 10th May (35th match)
2012 - 11th May (32d match)
2014 - 12th May (38th match)
2010 - 13th May (35th match) [started 20-15!]
2015 - 15th May (37th match)
2005 - 15th May (37th match)
2011 - 16th May (41st match)
2008 - 19th May (46th match)
2007 - 25th May (49th match)
2006 - 26th May (49th match)
2009 - 19th June (66th match)