I don't doubt you're all correct but we're talking about insulation resistance or integrity so maintain that if every circuit [4 circuits for example] IR tested say >200 Megohms you'd also see similar as a 'global' reading.
Insulation resistance is the same as any other resistance and follows the scientific laws governing resistance.
Getting a result which displays on a meter as >200megOhm just indicates that the resistance is higher than the maximum reading that instrument is capable of, an instrument with a greater scale would return an actual value for it.
You may very well get a global test result the same as each individual circuit, but that could be that the global result is actually 201megOhm and the individual circuits are all 1005megOhm
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