Are there better standards or documented best practices for larger hydrogen storage quantities than those in NFPA 2?

There is technically no upper limit for GH2 storage listed within the separation distance tables within Chapter 7 of NFPA 2. For LH2, there is a 75000-gallon upper limit for the LH2 storage separation distance tables within Chapter 8 for LH2. 
It’s important to note that many facilities have site specific issues such as large quantities, confinement, and congestion, so it may be applicable to apply contemporary engineering dispersion and radiation models to fully assess risk.
ISO TC 197 is actively developing LH2 tank standards based on recent research results in the European program described at http://preslhy.eu/. This process is usually slow because of the many nations involved and time inherently needed to reach the consensus required by the ISO standard development process.