iPhoto dates question

[thebignewt#IM]

I tried to change the date/year on some photos because my digicam's dates were wrong. It said 2005. I changed the dates to 2012. Now the info says it was taken in like 1934. I changed it again to 2012, and now it says like 1887! I think I'm doing it right, but why are the dates doing that? Thanks in advance.