Clarification about FCC exemption for subassemblies
From my experience with this (several products, using various combinations of wireless devices), then if the wireless module you use (be it cellular, Bluetooth, BLE, Wi-Fi or ZigBee or ISM) includes an antenna, and the entire module (radio + antenna) has been tested per FCC requirements (and therefore has an FCC ID stamped on it), then you do not have to do any further testing.

Here is an exmple of the type of module I am referring to.  Note the chip antenna on the upper left corner.



Note the one pictured above is pretty much blank.  The real one I have on my workbench is covered with text and logos, including an FCC ID and CE mark.

As long as you have only one wireless device on your board, (and there are no other wireless devices on other boards) the person using it in their product should be able to use the FCC ID that is stamped on the module.

But, if you have a module that attaches to a separate antenna, and only the module was certified (or not), then you must test the combination together.  Furthermore, if you have more than one radio in the final product, then they must be tested together, even if they have been certified separately.

This is my understanding.  You should have it verified by someone else before proceeding.