Answer: The mounting holes are a clear contact area for braided contact to a cover.
You won’t find any online because these are all custom designs. The above is just a simple rectangular shape.
When you mix logic speeds and RF frequencies which both overlap here in this design up to 6 GHz range for these types, you need a good common ground with many layers yet isolate the logic impulse currents from conducting through the RF grounds.
So you will see microvias every \$\lambda/20\$ for the highest frequency of interest, to reduce the loop crossectional area of these logic current spikes (CMOS FETs have capacitance when switched).
The surface is likely immersion gold-plated copper to buried layers to reduce oxidation and prevent irregular thickness solder level plating that affects impedance of transmission lines.
You will not see microvias for all the linear RF stuff because their ground plane is isolated from logic ground plane. and they are only connected near the RF ports. This minimizes the crosstalk of conducted and radiate ground currents between logic and RF.
The wide boundary around each zone is like the Mexican-US border. It sinks stray radiation fields, reduces crosstalk, but it doesn't stop migration of current or voltage fields it all together. It is coplanar after all and stray coupling is always reduced with a ground track in between. But the digital side is also analog with edge jitter and internal processes that are still sensitive to adjacent module crosstalk.
It is common for Faraday shields to be soldered on top when needed to further reduce crosstalk using reflow.
If you've seen a number of these boards without shields, then they did a pretty darn good layout design. Nortel and others also did some of these designs without shields up to 1 Gbit/s with very balanced differential microstrips (also bankrupt). I have some pre-Y2K designs we did for 1 GHz ISM band for the AMR market with in-house tin plated brass boxes etched by local PCB shops.
Unfortunately, this company went bankrupt. It had over 130 patents and many roots like HP microwave and a dozen others all experts in mobile wireless technology. Intel bought all the patents.