For my half season plan I got charged full price for 42 games, the game listing on the Nats Plus site includes the 4/2 exhibition game for both half season plans, so I was charged full price for this game. In my invoice from last August I was offered the chance to buy tickets for the 4/2 game for "half price" (the charge listed in the offer was closer to 25% of the price I was charged with my plan).
The invoice mentions that "The Friday [4/1] game is included in your plan". Kind of taking away the thrill of getting something free now since we were told it was included six months ago.
It appears that the Nats may have changed the plan so that both games are included. The decision to give tickets away for the 4/1 game is likely due to the lack of interest in the 1/2 price tickets. So for anyone who paid for the "second exhibition game special offer" I'm assuming that they got charged for full priced tickets as part of their 42 games plus the extras at half price.
Edit: In the past the exhibition game was half price, this year they have effectively made it buy one get one free. I always use the future game exchange program to swap the exhibition game for a real game and I'm sure I'll do the same thing this year for the 4/2 game. The 4/1 game is not listed on StubHub, they have a partnership with the team so it is likely that the Nats did not make that game available for exchange. I would not be surprised if there is a higher demand for this game due to the general admission seating and ticket groups having more members who want to attend than tickets allotted.
Edit: Saw a rumor on Twitter that the Nats will have Giolito pitch the 4/1 game.
Edit: A night game on 4/1 will have low temps, why not turn on the heat in the Stars and Stripes Club and allow fans to hang out in the comfort of the bar areas?
http://washington.nationals.mlb.com/was/ticketing/season_plans.jsp