My client cut a check on December 31st 2009, but I didn't get it until January 4th 2010. In my opinion this is 2010 income and they are puting it on the 2009 1099. One IRS agent says they can if the check was cut on the 31st, but another IRS agent says they can only if they can prove they attempted to mail it or have it picked up on the 31st. They said the info on it is in PUB 17. Do you have any knowledge of this. I already contacted the client, but I dont think they are going to correct it.