Are there other documents that relate to NEBS?

Yes.  There are other documents that relate to NEBS.  A very important sister document is GR-1089-COREElectromagnetic Compatibility and Electrical Safety - Generic Criteria for Network Telecommunications Equipment.  Together with GR-63-CORE, these 2 documents make up what's known as the "NEBS Criteria".

GR-1089-CORE details Electromagnetic Compatibility (EMC) and Safety requirements, including:

Another important document is GR-78-CORE.

This document consists of manufacturing and product design guidelines.

To get a full appreciation of all the documents related to NEBS, check out  Telcordia's "Family of Requirements" FR-2063.

Go to the following link and type "GR-1089", "GR-78" or "FR-2063" in the "Product Search" window to obtain ordering information:  Telcordia Store Link