I think it's safe to say that Nintendo has give us its 1st half 2019 games. Until Mario Maker drops in June, Yoshi's Crafted Story will be the only new big hitter released, with New Super Mario Deluxe and Box Boy supplementing it. I don't think we'll see anything added to the release schedule for those months. If you disagree, tell me, but I feel on solid ground moving forward with that assumption. That leaves the following 2019-confirmed games to be released in a six month timespan.
Do we see the problem here? If we include Astral Train (which I suspect Nintendo helped pay for and will publish), Nintendo's got at least seven major games to release in six months. Eight depending of how big Town will be.
Will Nintendo actually go through and publish all of those games by the end of the year, or will a couple of them slip into Winter/Spring 2020? Or maybe Nintendo won't consider Daemon X Machina and Astral Chain competition and will go ahead and release competing 1st party games against them?
Think instead of "once a month" "once every 3 weeks or so" and your problem is solved.
If anything were to slip, I'd say probably Town.
But Nintendo will not be alone this year pumping out great games for the system. Dragon Quest Builder 2 and XI S, Marvel Ultimate Alliance 3, Hellblade, possibly Doom Eternal, so this Summer and Fall will be stoked with games.
The Nintendo eShop rating Thread: http://gamrconnect.vgchartz.com/thread.php?id=237454