In former versions ( < 6.2), each agent collected the host metrics of the host, it is running on and stored this data on the system profile, it is connected to. So, if on one host several agents are running, reporting to different system profiles, than the data of one host has been stored several times.
With the new architecture ( >= 6.2), these host metrics are stored in the Infrastructure system profile. As host metrics with the same name and the same host source are now connected to the new infrastructure profile, the 'old' data is not longer accessible, as the id's beyond the metrics are pointing to a new infrastructure profile.
For further information see the documentation for the new infrastructure monitoring feature.