The Nanoha franchise has always been a strange one when it comes to how it approaches new content.
It has two narratives - Original and Reboot.
For the original, you get one narrative, that starts as an anime, but switches to a manga (and fills in a lot of gaps with sound stages). But there's no
adaptation here - Anime bits don't get a manga adaptation (to the best of my knowledge), and manga bits don't get anime adaptation. Nanoha fans are just expected to follow the continuing narrative from one medium (anime) to the next (manga) to the next (sound stages).
For the reboot, it's all animated movie, so far. The movie does have manga adaptations of it, though, IIRC.
Why the Nanoha franchise does things this way is anybody's guess. Sales aren't the reason though. StrikerS sold better than Nanoha A's which sold better than the original Nanoha. In other words, the anime just improves from one Nanoha show to the next when it comes to sales.
And Dog Days is what happens when you take Nanoha-caliber action scenes but remove the slightest ounce of suspense from them, since contrary to what Shirou Emiya says, ...
Dog Days also ramps up the ecchi big-time compared to Nanoha. I'm pretty much with Kaijo on Dog Days, I suspect.