Archives corresponding to the same <domain>_<disease study>.<platform> will have one and only one corresponding mage-tab archive. Conventionally, the serial index of the mage-tab archive is 1, however, the serial index is chosen by the submitting center.
For other archive types, the serial index is a number that uniquely identifies an independent data set from a particular experiment. There is no overlap of data files between archives of differing serial numbers. A numbering is entirely up to the data submission center. In general, BCRs use a serial index equivalent to a batch number while other center types start serial index series from 1.