maybe you missed the _point_ of the riddleIndeed. I was not aware of that. Did you post the "READ FORMAT CAPACITIES:" of a dvd+rw-mediainfo run on such a media ? I remember to have seen some which report "unformatted" as state and offer some formatting descriptors. (None with 4 GB, though.)
No, but BD-R[E] format capacity descriptors are more like guidelines. Specification permits you to specify any value between minimum and maximum (which you find among descriptors returned by the unit) with granularity of 256 clusters. Indeed, here is output for media formatted with -ssa=4G:
INQUIRY: [MATSHITA][BD-MLT SW-5582 ][BZE6] GET [CURRENT] CONFIGURATION: Mounted Media: 41h, BD-R SRM+POW Media ID: PHILIP/R02 BD SPARE AREA INFORMATION: Spare Area: 999424/1998848=50.0% free POW RESOURCES INFORMATION: Remaining Replacements:16843040 Remaining Map Entries: 0 Remaining Updates: 0 READ DISC INFORMATION: Disc status: appendable Number of Sessions: 1 State of Last Session: empty "Next" Track: 1 Number of Tracks: 1 READ TRACK INFORMATION[#1]: Track State: invisible incremental Track Start Address: 0*2KB Next Writable Address: 0*2KB Free Blocks: 10220544*2KB Track Size: 10220544*2KB FABRICATED TOC: Track#1 : 14@0 Track#AA : 14@10220544 Multi-session Info: #1@0 READ CAPACITY: 10220544*2048=20931674112 Compare to descriptors offered for blank media: READ FORMAT CAPACITIES: unformatted: 12219392*2048=25025314816 00h(3000): 11826176*2048=24220008448 32h(0): 11826176*2048=24220008448 32h(0): 5796864*2048=11871977472 32h(0): 12088320*2048=24756879360 Note READ CAPACITY return value being off by ~4GB from unformatted. A.