2/ Is most likely the reason Andy gave for the difference. The name "4.7" is not used in any Japanese OOB I have but I only have back to 2004 and they are named 120mm which is what 4.7 is so either the name was 4.7 when the scenario was built twenty years ago or the unit was modified to not have armour and the name was changed at the same time so that one I will leave as is. The "tell" for that is shown in Scenhack which shows a YES under Changed? which indicates that unit
had been changed along with a few pillboxes so that means it WAS the scenario designer who changed it
EDIT: Next time you see something like that, open up the scenario with scenhack and check its "changed?" status. If it reports YES it's a scenario designer change so intended and it does not need to be reported unless it's doing something highly unusual.
...and if you play this series in sequence there are quite a number that will not agree with the current encyclopedia because they show YES for changes made by the designer.
1/ however is a mystery. The sound number assigned now is an HMG sound and that unit has been a twin 13mm MG for as far back as I can check but you are correct, it produces a high-velocity cannon sound but that I can correct by "changing" them to the same unit using Scenhack ( which I have now done ) and they now play the correct sound FX but in the process of that fix I discovered we had two Japanese twin 13mm AAMG's..... the problem is that one of them is only a single and the photo for it is a single so I removed "twin" from the unit name.
Also, there are 13mm AAMGs in the next one but they give the correct sound in the test I ran