Uh, hey, Nova Cannons were perfected in the 37th, but did they have them when the Crusade started? I mean, Lances seem to have Frigates whose sole purpose is to wield one, but while the Lance is essentially a massive laser blast meant to pierce armor, it doesn't really have recoil due to being a laser so you could theoretically mount it on anything big enough and practically every military ship is big enough. Nova Cannons, on the other hand, take forever to reload, are inaccurate, have too much recoil to be mounted on anything smaller than a Cruiser even with design compromises made to help with that, and aren't really good against loose formations, but static defenses like you'd find on a planet don't really have as much of a problem with that, and unlike lasers, ridiculously huge physical shells don't have to worry about atmosphere compounding the Warp debuff on orbital bombardment.
Speaking of which Lances don't seem to have a specific date mentioned on their adoption.