The Japanese soldier would not surrender after the war, the rifle had the Emperors symbol on them. In order to facilitate the surrender and not disgrace the Emperor, the Americans / Japanese ground or altered the Mum. Circles around the mum can mean it was issued to a school, but it's not set in stone, it is conformed for school use if the Mum was circled and had this
stamped above the rifle type designation.
Generally the Mum that has circles around it means it was sold out of service to a foreign power. As in the Type 38s left for Siam by Japanese troops (Siam being a Japanese allie) had the mun circled with a small ring of circles.
As for the Type 99, not all models had the mono pod or anti aircraft sights. The first series produced did have the mono pod and anti aircraft sights, but as war moved froward this provision was dropped with an option to install them. Later series dropped the option all together as the last ditch rifles came to fruition.
Interesting fact, I have two Type 99s, they type 99s have chrome bores, one has a chrome bolt face. A curious note, some people seem to think the rifling it very badly worn, but my reading into this is the rifling is a hybrid of land and groove + a style of metford rifling basically polygonal rifling. Interesting and in my view brilliant. Hot damp constant wet and the elimination of the sharpe groove in the lands of the rifling.
Adding, Japan abandoned chromed bores in late 1942 early 1943, they simply could not afford to use chrome that way anymore . Note, very few type 38's are found with chrome bores.
Good web sites with Japanese markings and info.
ht tp://www.radix.net/~bbrown/japanese_markings.html