The good news for Yahoo! shareholders is that their stake in YJ is worth $8.2 billion today vs. $5 billion a year ago. Net of taxes and fees, that YJ stake is worth $5.07 per Yahoo! share vs. $2.83 per share a year ago.
Where are you getting those numbers? On earnings, as of 12/31/2012, the Yahoo Japan stake was worth $6.570B and with a 15% pop yesterday it takes it to $7.555B, an area where it was a few months ago. As of March 3/31/2012 slide 13 of Q1 2012: it was $6.547, a change of $3M in 9mos. I'll go back further just for you and that requires the annual report. In the 2011 Annual Report on page 84, in the middle, it says their stake in Yahoo Japan was worth $6B.(Dec 31st 2011). I even looked at the 2010 Annual Report and on page 77 as of Dec 31st 2010 it was $8B. In none of that do I see a fall to $5B and seems to below what it was a little more than 2yrs ago. You're welcome!