The Comet has NO PROJECTILE. What you're actually seeing is a tracer FX, same as for small arms fire. Tracers have no physical collision, so if the Comet's shot misses and scatters, the scattered tracer cannot collide with anything and trigger a hit, even if the tracer collides with the same tank because the scatter distance wasn't enough to completely avoid it.
I noticed this while testing units in Worldbuilder earlier, I tried to make a Firefly shoot at a truck (map prop) and the shots would just vanish into thin air before even reaching the truck. I assumed it was a bug and that the Firefly's shell just was set to phase through ground / props. I didn't consider the fact that it didn't have a shell at all, that's strange.
Also discovered that at one point they were considering (or might still be considering, for future DLC) the Archer tank-destroyer and the Humber armored car, since weapons for both exist.
Would like to see the Humber as a stock unit, so going Bofors doesn't leave you without any non-doctrine vehicles until T3. Speaking of unused things, there is also a British Tank Crew, British Churchill Crew, and a Supply Universal Carrier.
The 9.75 inch flame mortar ability refers to an experimental Valentine that was in development but never produced, and an EBP for it exists (though no model, it's got the Priest as a placeholder), so at one point they were thinking of that ability being a tank call-in rather than an off-map artillery attack.
Probably cut because it wasn't used. The moment they throw in a unit that wasn't actually used in the war, they open the flood gates to "GIVE IS-3, GIVE T-44, GIVE MAUS, GIVE T28 SUPER HEAVY ASSAULT TANK". Not a good thing to open up just because you wanted a Mortar Tank...