Did you also adjust for inflation in there? If not, there's an additional ~10% that can be adjusted for. $44.6B in 2008 would be $49.84B in 2016 USD, an even wider gap.
But there are fewer shares because yahoo "returned" north of $10B to investors through share buybacks. Not exactly sure how that should be accounted for, but I think relevant to the calculation.
It is best to look at market cap to determine value - Microsoft's 2008 offer was $44.6B; Yahoo's current market cap is $41.65B.
The discrepancy from then to now comes from the number of shares outstanding. There are fewer outstanding YHOO shares today than there were in 2008.