I'm currently using yahoo.finance.historicaldata table through YQL to retrieve historical quotes informations.
It appear's that table content changes randomly for symbols where split or merge opérations occurs.
Sometimes quotes seems not to take into account split/merge ratio, quotes are then what they was in the past,
sometimes, these ratio are applicated on the historical quotes.
Example for symbol AKKA.PA where a split (2:1) occurs on 08/20/2007 :
If I retrieve quotes for these symbol at 08/17/2007 I get 15.70 (open), running the same request in march these year, , I had 31.40 (open) !