It appears the approval was given on August 31st, but for some reason the news is just leaking out now. In any case, there hadn't been any official announcements by Toshiba or the DVD Forum prior to the leaked information.
The 51 GB derivative enables three layers to be
bonded together within the same 0.6 mm substrate limitations as
standard discs, with varying reflectivity for each layer that enables
contents from buried layers to be revealed, even through the bonding
material. Multi-layer bonding is not a novel process, though the
reflectivity formula is. Engineers from Warner Bros. have filed patents
for similar multi-layer bonding concepts including, according to
patents, a four-layer process, though recent events lead to the
conclusion that Warner isn't interested in exploiting its own
intellectual property, at least presently.
Also, in an apparent escalation of the format wars, Warner Bros. was reportedly offered cash to switch from supporting both formats to supporting HD DVD (by Toshiba, naturally).