I don't know how the 'augmentation' principle would work with IJA divisional definitions. Perhaps Cat "A"s could have a couple device slots that are at 0 for most others. The JP 82mm, for example; it wasn't authorized at divisional level, but we encountered it often; or was it the 70mm trench mortar we encountered? It's very noteworthy that throughout the entire Pacific Campaign, the 81 or 82 mm mortar (per se) was not included in any casualty/effectivity analysis performed by either the USMC or the USA.
The 70mm, 82mm and 81mm mortars represent three (or 3.5) generations of Japanese medium mortars. They had the best light mortar in the world - according to one historian who did US, Australian and Japanese armies in his book (Touched With Fire).
But that was a squad level weapon - something we do now - but didn't then! For company or battalion, they used medium mortars. The 70mm is just the oldest of these - a WWI era device. The 82 mm was a Japanese development - a copy of an 81 intended so we could not use their ammunition. But eventually they went over to 81 mm anyway. The first try was too heavy, so they cut it down, and got a rather fine weapon with almot the same performance but easier to carry than most. For that reason it was popular - and you ran into the older mortars only if the new ones were not available (which was often). The Navy, for example, was only given ex-Army 70 mm, and they put them in small detachments of 2, with lots of men to carry them (being heavy). [An IJN "heavy weapons company" usually had one "platoon" of 2 70 mm mortars and one "platoon" of 2 37mm rapid fire guns - these being an older weapon than the German 37mm ATG - a WWI era trench gun. Curiously, my own regiment today has a battery of 19th century 37mm guns - almost the same weapon - there are four - and they are provided with cannister shot - something I didn't realize such weapons had.]
