The Aggregator meter is a Summation Meter (a Virtual meter, that is the summation of a bunch of input meters, defined as a Meter Account). When a component meter calls in, it adds that new profile to itself. If you move the maxdate back on any component meter, it invalidates the data back to where you set the maxdate back to, and recalculates the profile on the Aggregator again.
Furthermore, it is a Summation Meter on a Meter Account, that is set for Net metering, which means that we don't just total opposing energy values, we get the difference per half hour (sample period of Summation Meter, co-inciding with Period of Meter Account) and if negative put it in export energy and if positive put it in import energy
Does that give some perspective?