I ask them and this is what they told me:
The cumulative performance gives the entire performance and does not
distinguish between first or subsequent attempts.

The first % is more reliable as it gives you an indication about where
you\stand. If your cum performance later increases to 70% it might be due
to familiarity with the question and hence might not be accurate.

Yes. If you repeat a block of used questions then the performance is
counted towards the cumulative performance.

The best way to go through the QBank and measure your performance is to
go through all the unused questions first. That will give you an idea
about where you stand in terms of preparation and identifying the
subjects you might be weak in.

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