LOBs are never stored as part of the physical row of the data subtable, but are implemented as LOB subtables. So there will be a LOB subtable for each LOB column in the table.
The primary data row is linked to the subtable record by means of an Object identifier (which is stored in the actual primary data row).
Within the LOB subtable, if we take a single LOB value into consideration, it's contents would be broken into multiple rows internally and given a sequence number to each row (this structure is transparent to user for all practical purposes).
The subtable row structure will have a rowhash (same as primary data row rowhash), uniqueness value,sequence fields in it's row header. The rowhash + uniqueness value will be the same for all the rows belonging to the "Same" LOB value's contents. The sequence is used to identify the order of records for the given LOB value.
The sequence field is 15 bits, so you can have 32K recs for a single LOB value. So if we take max row size (64k) into account, then we have the largest possible LOB to be 32k*64K = 2GB.