As long as we are talking about the side mount, let's not forget the fact that currently, the only accessory that can legally be put on a side mount is a gun cam - since all the other accessories specify which mounts they are allowed on, and the gun cam is the only one that mentions it.
So, you can house rule which accessories go on the side mount, but by the RAW, the gun cam is it.
There are also a few mods that don't describe where they can go at all. Like the commlink. Makes me think you can mount ones that don't say specifically on any of the mount locations.
I dunno. Given the ones that can go anywhere tend to specify such... I think these are in the slotless category. Especially since they include things like the weapon personality, which is basically just a program.
That's not true. They specifically call out the ones that don't eat up a mount location, like the concealable holster or sling. While something like the commlink or flashlight don't get any mention to where they are mounted, so theoretically can go anywhere.
And while it maybe completely ridiculous to have a flashlight on your stock, it does make sense that you'd be able to mount it on over, under, on top, or inside the barrel or inside the internals of the gun (somehow). There might even be some kind of half logical explanation to get a stock mounted flashlight to shine in front of you somehow.
And yet, the weapon personality is software and not marked down as slotless. Given everything else that takes up a slot is hardware, that one item doesn't make sense as taking up a slot. Because it's physically impossible to mount a program to the side of a physical object. You can attach an RFID tag holding the program, but RFID tags are hinted (through both fluff and the rules for the Tracker mod) to be slotless.
Also, mounting a flashlight to the stock portion of the gun means the flashlight will either have its beam blocked by the gun or it will illuminate things behind you, while using it to modify the barrel means it will likely be destroyed the first time you pull the trigger. Some would say that the flashlight is mounted beneath the barrel when put in that position... except that underneath the barrel happens to be an entirely different slot. Above the barrel puts it in top of the weapon slot. Basically, anything that is mounted on the barrel slot needs to be designed with the idea a bullet will be traveling through it. And the commlink is in the same boat.
The problem with those items going in any slot is that it doesn't actually make any sense. Then again, look at the foregrip item; given the way the slot system is written up, the foregrip has you holding the barrel of the gun in your hand. It is obviously an item that belongs in the underbarrel slot.
Edit: And, looking at it, you are right that the items which are slotless are marked and there's no item marked as going in any slot (except one possibility, and it runs into the same problems as the flashlight).
