Fiber exposed on board edge

IPC-A-610F 10.2.6 Laminate Conditions - Depanelization talks to the acceptability of the depanelization criteria for assembled boards. There is no requirement for moisture sealing with epoxy or other material. Basically, the standard requires that the depaneling process shall not affect the intended form, fit or function of the assembly. The standard is more specific than that, as you would expect. Consider the standard a good read.

IPC-A-600 talks to the depanelization of bare boards, also a good read.

Finally, don't expect the solder mask on your assembly to be a moisture barrier. It's a solder mask. That's it. Some people conformally coat their assemblies to provide for environmental protection.

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