I believe the problem is that there is a difference between integral and internal.
To me, for what it is worth, integral means that you can't remove it - but doesn't actually mean that it takes up the internal spot.
For example: the Ares Crusader MP has a "integral barrel-mounted gas-vent 2 recoil compensation system"
So integral and internal are not the same thing.
To me, this means that you can't just take the gas vent 2 off of the Crusader and slip on a suppressor - the barrel mount is used up by the integral gas vent 2.
Similarly, they Steyr TMP has a "built-in top-mounted laser sight." - to me, this means that you can't remove, and it occupies the top mount - so integral, but not internal.
Now, if it doesn't specify a mounting, then an integral item could be internal, and in many cases, has to be. For instance, the Ingram Smartgun, comes with a gas vent 2 (barrel mount), a smartgun system (top mount) and an integral sound suppressor - which in this case must be the internal mount, since the barrel mount is occupied.