Connectors need to be installed with the clamping means external to the box to be installed per the listing and labeling. The do make snap in non-metallic clamps that can be installed from inside the box for situations where you don't have access to the exterior of the box.

You are required to secure the cable to the box per the last sentence od 314.17(C). The exception is for 1 gang boxes where you are able to secure the cable within 8" of the box measured along the cable.

I have not seen a "Listed" multigang NM cable box that didn't have clamps. Possibly I'm in need of an update [Linked Image]

As for the box behind the fluorescent fixture look at 410.14(B)

George Little