Mark Ode is an industry respected person who has authored many articles.
That said, if you can't locate the mfg data (doubtful if older equip) you could probably find it at the mfg website. The info (curves, etc) for the exact MCB you have.
IMHO, a qualified testing company would be the way to go.
The 'age' of the MCB could be a factor, or someone played with the GF trip setting, or previous faults tripped the branch cb.
I had a old, 2 lamp, F-96 slimline, 277 volt ballast that self destructed, and took out the GF main (2000 amp). No branch cbs tripped, ad yes, this was an 'old' facility with a new 2000 amp service.
Hope my opinion helps
