A question about the 'Epochs and the Sequencing Window' section in the overview.md

[Nickqiaoo]

The diagram describes how L2 blocks are derived from L1 blocks.I am puzzled about B1 in the diagram. Does 'B1' here stand for batch data? It seems in the diagram that the L1 origin of the L2 block includes the batch data for this epoch.Does The L1 origin should never contain any data needed to construct sequencer batches？