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-CORE,  Electromagnetic 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:

• Electrostatic Discharge (ESD)
• Electromagnetic Interference (EMI)
  • Radiated Emissions - (Electric Fields)
  • Radiated Emissions - (Magnetic Fields)
  • Conducted Emission (AC Power Leads - Voltage)
  • Conducted Emission (AC and DC Power and Signal Leads - Current)
  • Conducted Emission (Analog Voiceband Leads)
• Lightning and AC Power Fault
• Steady-State Power Induction
• DC Potential Difference
• Electrical Safety
• Corrosion
• Bonding and Grounding

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.